Ich gehe durch den Park.
English: I walk through the park.
In German, some prepositions always use the accusative case. These prepositions are called 'accusative prepositions.' They affect the article and pronoun that follow them.
Use these prepositions when you want to show movement, direction, purpose, or opposition. The noun or pronoun after these prepositions must be in the accusative case.
Ich gehe durch den Park.
English: I walk through the park.
Das Geschenk ist für dich.
English: The present is for you.
Wir spielen gegen die Mannschaft.
English: We play against the team.
Er fährt ohne seinen Freund.
English: He travels without his friend.
Wir sitzen um den Tisch.
English: We sit around the table.