Accusative case - biernik

 The accusative case is used for direct objects of positive or affirmative sentences.  Which are sentences expressing something that is so, that is fact, that is happening, like

Piję kawę - I'm drinking coffee

as opposed to negative sentences, which would state the reverse and have the direct object in a different case.

The accusative case is also used when saying something on a certain day of the week, like:

w poniedziałek - on Monday

we wtorek - on Tuesday

w środę - on Wednesday

w czwartek - on Thursday

w piątek - on Friday

w sobotę - on Saturday 

w niedzielę - on Sunday

After the following prepositions when used with verbs expressing motion :

po - to get someone / something - eg: Idź po mamę (go get Mum)

na - on / to - eg: Połóż na  stół! (Put it on the table!)

w - into - eg:  Proszę skręcić w aleję Wolności (turn into aleja Wolności)

otherwise they need the locative case after them.

and also after these prepositions when used with verbs expressing motion:

przed - in front of / outside

między - inbetween

nad - above

pod - under

which would otherwise need the instrumental case after them.

and after:

przez - through