In Polish, one pronounces every letter (apart from the combinations ch, cz, sz, dź, dż and rz) separately.

Vowels: 

a	as in hat
e	as in met
i	as in meet
o	as in pot
u	as in whose
ó	as in pool
y	as in dim

There are also two nasal vowels in the Polish language: ą and ę. 
ą is pronounced as "on", like the French nasal o. 
if the ą is followed by a "b" or "p", it is pronounced as "om"

ę is pronounced as "en", like the French nasal e. 
As with ą, the ę is pronounced as "em" before "b" or "p". 
A final ę is pronounced as a usual Polish "e". 
 

 

Consonants: 

c	"ts" as in cats
ć, ci	as in cheese
ck	as tsk
cz	as in chair
ch	as in loch
dz	as in goods
dź, dzi	as in jeans
dż	as in jam
j	as in yes
l	as in last
ł	as in winter
ń, ni	as in onion
rz	as in pleasure
ś, si	as in sheep
sz	as in show
w	as in van
ź, zi	as in Rhodesia
ż	as in pleasure, same as rz

all others are pronounced as in English.

Two identical consonants following each other are pronounced separately. e.g.: An-na

Once in a while the pronunciation of consonants may change: they can either be voiced or voiceless. 
The most common shifting is the devoicing, this means a voiced consonant is said as it's voiceless counterpart. 
This happens at the end of a word or when standing before a voiceless consonant.

 

When ś, cz or k stand before an voiced consonant except of w and rz they are pronounced as their voiced counterpart. 
Here is a list of all pairs: 

voiced	voiceless
b	p
d	t
g	k
w	f
z	s
ź	ś
dz	c
dź	ć
ż, rz	sz
dż	cz

if a consonant is followed by an "i" it is softened.

Stress:

Usually the 2nd last syllable is stressed. 
But there are also a few cases in which the 3rd last syllable is stressed. Usually these are foreign words. 
If a monosyllabic preposition and a monosyllabic pronoun stand together the preposition is stressed. The same happens with the combination nie and verb.