Prepositions in German are an intriguing sort of torture. Prepositions on their own are often bad, since they rarely translate directly into other languages. Just try it with a handful of French and English ones.
German adds to this problem however, by tying prepositions to cases. There are prepositions which take the accusative case, prepositions which take the dative case, and prepositions which take either the accusative or the dative depending on whether there is motion. And if it confuses you to read that, just try putting it to use in a sentence.
English is blissfully simple in comparison.