The direct object of most verbs; the object of some prepositions.
Answers the questions: What is the action is about? Whom the action is about? I see the tree. I see what? The tree. I see Mark. I see who? Mark. We would like to visit Krakow . What would you like to visit? Krakow . I have a new dress. What do you have? A new dress.
Most common verbs used: I see, I have, I like.
Other examples: I am going to buy a plane ticket. I am going to buy what? A plane ticket. I am going to sell my car. I am going to sell what? My car.
The accusative also follows preposition that indicate going towards or motion. Pzez-through Na-on, to, towards, for I am going to the market. I am waiting for my love. I will be on vacation. I am walking through the building.Incidentally, the most common Polish cases are the nominative (dictionary form) and accusative, which account for almost 65% of the Polish cases. The nominative, accusative, genitive, and locative accounts for over 90% of the Polish cases. But you still have to learn them all :-)