Prepositions
A prepositional phrase in Latin is made up of a preposition followed by (usually, but there are a few postpositives) a noun phrase in an oblique case (ablative, accusative and rarely genitive). The preposition determines which case is used, with some prepositions allowing different cases depending on the meaning. For example, Latin in takes the accusative case when motion is involved (English into) and ablative when it indicates position (English on or inside of).
Read more about this topic: Latin Grammar