All the prepositions can be used to specify a *location*: Wo ist meine Brille? Where are my glasses? Sie liegt auf dem Tisch. They are on the table. -> "auf = on (top)" Sie liegt im Badezimmer. They are in the bathroom. -> "in = in" Sie liegt am (=an dem) Fernseher. They lie next to the TV. But: Ich habe viel Geld auf dem Konto. I have a lot of money on my account. In addition these prepositions can also be used differently. For instance they can also indicate a direction: Ich gebe das Buch an meinen Bruder. I give the book to my brother. Wir gehen in die Berge. We go into the mountains. Ich klettere auf den Baum. I climb on the tree. Hopefully these examples give you some indication about the use: "auf" usually implies "on (top)" or an upward direction "in" usually implies a location surrounded by something I know, prepositions are very hard! I am learning Dutch right now and although German and Dutch are quite similar I am always confused about the different use of prepositions. Good luck for your studies!