Nouns

Unlike in the English language, nouns do change in different contexts. A noun depends on it's case which again depends on the gender, number and position of the noun.
The three genders are: masculine, feminine and neuter. There are all together 7 cases in Polish: nominative, vocative, accusative, genitive, locative, instrumental and dative. Unfortunately there is a number of nouns that are declined irregularly.
 

Diminutives:
This feature denotes the smallness or fondness of a person or object.
For ordinary nouns:
Nouns whose stem is not ending k add "ek" for masculine, "ka" for feminine and "ko" for neuter nouns.
Nouns whose stem is ending in k or c add "czek" for masculine, "eczka" for feminine and "eczko" for neuter nouns while the k or c disappears. These endings can also be used to form the diminutive of a diminutive. In some cases the noun turns out to be not pronounceable, then you use the endings "szek", "szka" and "szko" instead.
Masculine nouns in c, cz, rz, sz add "yk" - for further diminutives use "yczek"
Masculine nouns in d, j, ł and t add "ik" - for further diminutives use "iczek"
For proper names:
Here you add "ątko", "cia", "ina", "la", "unia", "sia" or "zia". Male proper names take usually "ek", "io", "iu" or "uś". The form "ocha" is only used colloquially and pejoratively.
 

Gender:
masculine: these nouns don't have a ending as such, they usually end with a consonant, a few also with a vowel. Some nouns and with an "a", these are declined as feminine in singular but as masculine in plural.
feminine: these end with "a", some also with "i" or "ść" - but there are some others that end with a consonant as well.
neuter: these have the endings: o, e, ię, ę and um
Masculine nouns denoting a profession, relationship or an animal can be changed in a feminine form:
nouns not ending "k" add "ka" or "anka"
nouns ending "k": "ca" or "czka"
But some nationalities' feminine forms are  formed by adding "owa" or "ewna".
Some feminine nouns end also in "yni"
A few nouns can't be changed, so you have to add "pani" to that noun.
 

Nominative case:
The singular is the standard form of the noun.

Plural:
Masculine: (not men!)

after hard consonants except k and g	+y	dom: domy
after k or g	+i	bank: banki
after c, cz, dż, j, l, rz, sz or ż	+e	hotel: hotele
some nouns in b and p plus those ending in a consonant with an accent (which is lost then)	+ie	karp: karpie

these vowel changing occur for the last stem vowel:
ó -> o
ą -> ę
Masculine: (men)

titles, professions, family members, some nationalities and surnames (except those in ski, cki and dzki)  an accent is lost and a additional i inserted	+owie	pan: panowie Arab: Arabowie
Nationalities in "in"	replace the "in" with "ie"	Amerykanin: Amerykanie
after cz, j, l, rz, sz and nouns in accent	+e	przyjaciel: przyjaciele
after hard consonants (final consonant often changes)	+i	student: studenci
after k, g or r (final consonant changes)	+y	Polak: Polacy
after c, iec and niec c->cy; iec-> cy; niec->ńcy	+y	Niemiec: Niemcy

Those consonant alternations occur:
k: cy
g: dzy
r: rzy
t: ci
st: ści
ch: si
d: dzi
z: zi
ł: li
Feminine:

after hard stem (except k and g) + a also nouns that end cz and sz	y	kawa: kawy
after ć, dź, ga, ka, ń or ść and some nouns in l or w (the accent is lost)	+i	nić: nici
after c, ca, cz, i, ia, ja, la, rz, rza, sza, ż, ża, dż	+e	noc: noce
after nouns ending in a noun having an accent, which is lost ó->o; ą -> ę	+ie	jesień: jesienie

Neuter:

nouns in o, e, ie and um	a	kino: kina
most nouns in ię	iona	imię: imiona
nouns in ę	+ta	cielę: cielęta

Vocative case:
This case is used to address people, animals or objects. But in case you call someone you use the nominative case. Usually in colloquial language you don't use this case at all - and rather the nominative. In greetings with Pan, Pani or "Państwo" the dative case is used.

Singular:
Masculine:

after hard consonants except k and g	+e	kot: kocie
after c, ch, cz, dż, g, j, k, l, rz, sz and ż	+u	mąż: mężu
after a noun with an accent (which is lost)	+iu	liść: liściu
nouns ending ec	cze	Niemiec: Niemcze
nouns in a	o	tata: tato

Changings occur as in the locative case.
Feminine:

hard stem, c, cz, dżm rz, sz and ż + a soft stem + ia	o	mama: mamo
diminutives in ia	u	ciocia: ciociu
nouns in i or after consonants with accent (which is lost)	i	pani: pani pieśń: pieśni
nouns in c, cz, dż, rz, sz or ż	+y	noc: nocy

Neuter: do not change

Plural: as in nominative plural.
 

Accusative:
The accusative case is used for direct objects (not with negative verbs), in statements about health, after certain prepositions or for the period of an action.

Singular:
Masculine: (objects only!) This form doesn't change except fruits, vegetables, vehicles, units of currency, games, dances and cigarettes, these add an "a".
Masculine: (alive nouns) Those not ending in "a" don't change. Nouns in "a" change the a to "ę".
Feminine:

nouns in a	ę	kawa: kawę
nouns in i	+ę	gospodyni: gospodynię
nouns ending in a consonant	do not change	noc: noc

Neuter: do not change

Plural:
Masculine (not men!): use the nominative plural
Masculine (men and those ending in "a"): use the genitive plural.
Feminine: as in the nominative case
Neuter: as in the nominative case
 

Genitive case:
This is used to denote possession, for a direct object with a negative verb, after certain positive verbs, after number 5 and upwards, to express quantity, to express "some", for vague times and after certain preposition.
These alternations do occur:
o: ó    ę: ą    sometimes an extra "e" is added
when ending with a consonant: ó: o    ą: ę    sometimes a "e" is lost

Singular:
Masculine nouns:

most non-alive nouns and nouns in the u-list	u	dom: domu
alive nouns ending in a consonant and nouns in the a-list	a	pan: pana
alive nouns ending ga or ka	i	kolega: kolegi
alive nouns ending in a consonant (not g or k) +a	y	poeta: poety

Alternations:
iec, ec-> ca
niec-> ńca
ść -> ścia
ek -> ka
ier, er-> ra
U-List:
abstract nouns, collective nouns, substances, liquids, gases, many foreign words, cities, rivers and mountains plus nouns derived from verbs and days.
A-List:
fruits, vegetables, vehicles, units of currency, games, dances, cigarettes, tools, parts of the body, most Polish towns, units of the day and nouns ending in ek, ik or yk.
Feminine:

hard stem (except g and k) +a plus nouns in c, ca, cz, cza, rz, rza, sz, sza, ż, ża	y	noc: nocy
consonant +ja (the J is kept)	change a to i	Francja: Francji
vowel + (a)j  nouns in ea, ga, ka, l, la, ua and w nouns in b, c, m, n, p, s, w or z + ia after consonant with accent (lost)	i	idea: idei nić: nici
nouns in i	do not change	pani: pani
after ch, d, f, g, k, l, r or t +ia	change a to i	melodia: melodii

Neuter:

nouns in o, e or ie	a	kino: kina
nouns in ię	change ię to ienia	imię: imenia
nouns in ę	+cia	zwierzę: zwierzęcia
nouns in um	do not change	muzeum: muzeum

Plural:
Masculine:

after hard consonants and c, as well as with nouns taking the ending owie in the nominative plural ó: o; ą: ę or e	-ów	bank: banków
nouns in a	change a to ów	kolega: kolegów
after consonants with accent which is lost	+i	koń: koni
after j or l. the j is lost.	+i	hotel: hoteli
after cz, dż, rz, sz and ż	+y	klucz: kluczy

Feminine:

nouns with consonant +a, but not cja, sja or zja o: ó; ę: ą; sometimes an e is added	remove the a	lampa: lamp
nouns in i or ia but not nia	i or ia is removed, if possible the final consonant takes an accent	pani: pań
after c, cz, rz, sz and ż	+y	noc: nocy
nouns in nia	the a is lost	suknia: sukni
nouns in ea, j, l, ua and w. the j is lost	+i	kolej: kolei
after consonants with accent (which is lost) o: ó; ę: ą; sometimes an e is added	+i	pieśń: pieśni
foreign nouns in ia, cja, sja and zja	change a to i	historia: historii

Neuter:

nouns in o, e and ie sometimes: o: ó; ę: ą or an e is added nouns in cie and nie add a accent to the n or c	remove ending	lato: lat ubranie: ubrań
nouns in ię	change ę to ion	imię: imion
nouns in ę	change ę to ąt	zwierzę: zwierząt
few nouns of three syllables with soft consonants before the ending	replace ending with i or y	przymierze: przymierzy
nouns in um	change to ów	muzeum: muzeów

Some positive nouns require the genitive case instead the accusative. Here is a list:
bać się, brakować, bronić, chcieć, doczekiwać, domagać się, domyślać się, dotykać, dotyczyć, dożyć, najeść się, napić się, oczekiwać, pilnować, potrzebować, pragnąć, próbować, przestrzegać, pytać się, szukać, słuchać, spodziewać się, uczyć się, używać, wstydzić się, wymagać, zapominać, żałować, żądać and życzyć.
 

Locative case:
This case is only used after these prepositions: na, o, po, przy and w.

Singular:
These consonant alternations do occur:

b: bie	f: fie	k: ce	m: mie	p: pie	s: sie	w: wie	ch: sze	sł: śle	sn: śnie	zd: żdzie
d: dzie	g: dze	ł: le	n: nie	r: rz	t: cie	z: zie	dz: dzie	sm: śmie	st: ście	zn: żnie

And those vowel alternations as well:

ó: o

ą: ę

e: -

a: e

Masculine:

after hard consonant except ch, g and k and nouns ending in hard stem + a	e/ie	kot: kocie tata: tatcie
after ch, g, j, k and l - consonants to not change!	+u	bank: banku
after c, cz, dż, rz, sz and ż	+u	Niemiec: Niemcu
after consonants with accent (lost)	+iu	koń: koniu
nouns in ca, consonants do not change	turn a to c	kierowca: kierowcy

Feminine: This is the same as in the genitive case except for nouns ending in a hard stem + a, they change the a to e or ie.
Neuter:

after hard stems (except ch, g and k) + o	change o to e/ie	kino: kinie
after ch, g, j, k and l, consonants do not alternate	change o to u	oko: oku
nouns in e and ie	change e to u	życie: życiu
most nouns in ię	change to ieniu	imię: imieniu
nouns in ę	+ciu	zwierzę: zwierzęciu
nouns in um	do not change	muzeum: muzeum

Plural:

nouns not ending in a consonant with accent, ia or io	+ach	chata: chatach park: parkach
nouns ending in a consonant (which is lost) with accent or ia or io	+iach	koń: koniach
most nouns in ię	change ię to ionach	imię: imionach
nouns in ę	+tach	zwierzę: zwierzętach
a few country names	+ech	Niemcy: Niemczech

Instrumental case:
You use this case for the predicate of the verbs "to be" and "to call". For the time or duration of an action, for the means, route or tool used to perform this action. Plus it's used after certain verbs in prepositions.

Singular:
Masculine:

after hard stem except g and k	+em	pan: panem
after g and k, as well as after consonants with accent (which is lost)	+iem	Polak: Polakiem
nouns in a	change a to ą	tata: tatą

Feminine:

nouns ending in a or ia or in a consonant without an accent	ą	Polska: Polską
nouns in i or in a consonant with an accent (which is lost)	ią	pani: panią

Neuter:

after hard stem (except g and k) +o or e	em	okno: oknem
nouns in ie, go and ko	iem	jabłko: jabłkiem
most nouns in ię	ieniem	imię: imieniem
nouns in ę	+ciem	zwierzę: zwierzęciem
nouns in um	do not change	muzeum: muzeum

Plural:

most nouns	ami	kolega: kolegami
nouns in i, ia, io, ie and those in consonants with accent (which is lost)	iami	pani: paniami
monosyllabic nouns ending with a consonant having a accent	+mi	nić: nićmi
most nouns in ię	ionami	imię: imionami
nouns in ę	+tami	zwierzę: zwierzętami

Verbs that require this case: bawić się, być, cieszyć się, dysponować, interesować się, kierować, martwić się, napełniać, niepokoić, obciążać, obładowywać, ochraniać, obdarzać, ogradzać, opiekować się, otaczać, pachnąć, pokrywać, posługiwać się, smucić się, stawać się, sterować, władać, zajmować się, zasłaniać, zasnuwać and zostać.
 

Dative case:
This case is used for the indirect object and after certain verbs, impersonal expressions and prepositions.

Singular:
Masculine:

most nouns	+owi	student: studentowi
nouns in a consonant having a accent (which is lost then)	+iowi	koń: koniowi
a few old, monosyllabic nouns	+u	pan: panu
after hard stem + a	e/ie	tata: tacie
nouns in ca	change at y	kierowca: kierowcy

Feminine: same as locative singular.
Neuter:

nouns in o, e or ie	u	kino: kinu
most nouns in ię	ieniu	imię: imieniu
nouns in e	+ciu	zwierzę: zwierzęciu
nouns in um	do not change	muzeum: muzeum

Plural:

most nouns	om	kolega: kolegom
nouns in i, ia, ie, io and nouns ending with a consonant having an accent (lost)	iom	pani: paniom
most nouns in ię	ionom	imię: imionom
nouns in ę	+tom	zwierzę: zwierzętom

These verbs require this case: być do twarzy, darować, dawać, dawać znać, docinać, dokuczać, dziękować, dziwić się, grozić, kazać, meldować, mówić, nadawać się, odpowiadać, opowiadać, pisać, płacić, podobać się, pokazywać, pomagać, powiadać, pozwalać, pożyczać, przeszkadzać, przyglądać się, przykazywać, przypominać, radzić, rozkazywać, służyć, szkodzić, ufać, ulegać, wierzyć, wybaczać, zabierać, zadawać, zagrażać and życzyć.

Some irregular nouns:
dzień, tydzień, człowiek, pieniądz, rok, przyjaciel, brat, ojciec, ksiądz, orzeł, rząd, kwiecień, pan, pies, pani, gospodyni, ręka, wieś, rzecz, kolej, nić, dziecko, oko, ucho, książę, radio, studi, państwo and lato.