Ich stelle das Buch auf den Tisch.
English: I put the book on the table.
In German, some prepositions can be used with either the dative or the accusative case. Which case you use depends on whether the sentence shows movement (accusative) or location (dative).
Use these prepositions with dative when you talk about where something is (location). Use them with accusative when you talk about movement towards a place (direction).
Ich stelle das Buch auf den Tisch.
English: I put the book on the table.
Das Buch liegt auf dem Tisch.
English: The book is lying on the table.
Wir gehen in das Kino.
English: We are going into the cinema.
Wir sind im Kino.
English: We are in the cinema.
Die Katze schläft unter dem Bett.
English: The cat is sleeping under the bed.