This is the 275th most frequent Polish word.
piłkę
"Piłkę" means "ball" (accusative or singular form in Polish).
The word "piłkę" is used as the direct object, in the accusative case, reflecting what was kicked by Janek.
Janek kopnął piłkę do bramki.
Janek kicked the ball into the goal.
"Piłkę" is in the accusative case, indicating the object we purchased.
Kupiliśmy nową piłkę do siatkówki.
We bought a new volleyball.
Here "piłkę" is the object of the verb "widziałeś" in the accusative case, asking about the position of the ball.