Hey i copied a quora answer for you but he explains it very well. Im a german speaker btw
Answer:
Most common prepositions in German either always take Akkusativ or always take Dativ. The Wechselpräpositionen (an, auf, hinter, in, neben, über, unter, vor and zwischen) are the exceptions! They take Akkusativ when describing a destination (Wohin?) and Dativ when describing a location (Wo?).
One intuition that’s helped me as a native speaker of English is the comparisons between “in” vs. “into” and “on” vs. “onto”:
Use Akkusativ when the usage is like “into” or “onto” in English: Ich bin dann in das Zimmer gegangen. (“Then I walked in[to] the room.”) Könntest du das mal bitte auf den Tisch legen? (“Could you please put that on[to] the table?”) Ich habe heute nicht vor, in die Stadt zu fahren. (“I’m not planning on going into town today.”)
Use Dativ when the usage is like “in” or “on” (but not “into” or “onto”) in English: Ich bin den ganzen Tag in meinem Zimmer geblieben. (“I stayed in my room all day.”) Das liegt nicht ohne Grund auf dem Tisch. (“That’s on the table for a reason.”) Ich habe heute vor, in der Stadt zu übernachten. (“I’m planning on staying [lodging] in town tonight.”) Er guckte sich das Schild vor dem Haus an. (“He looked at the sign in front of the building.”)
[The rule only really directly helps with “in” and “on,” but hopefully with practice you’ll be able to extend that intuition to other prepositions. For example: Er stellte das Schild vor das Haus. (“He put the sign in front of the house.”) See how that “in front of” feels like “into” and not just “in”? You could just have well have said “in[to] the house.”]
