We know a preposition tells us the position of two things, in relation to each other. In this sentence, which two things are we relating? 'The man jumped into the river.'

A preposition is a word or group of words used before a noun, pronoun, or noun phrase to show direction, time, place, location, spatial relationships, or to introduce an object. Some examples of prepositions are words like "in," "at," "on," "of," and "to."