Answer :
Prepositions show location, direction and time. They are words that are being used to link phrases, nouns and pronouns in a sentence. They are placed before the phrase that is to be linked. Examples are at, to, in, on, from and the like.
I believe the answer is: They show location, direction and time.
In order to show this, prepoisition usually made from the combination of noun , pronoun, or noun phrase, which called its complement, or sometimes object.
Example of prepositions that show location : under, on top
Example of prepositions that shows direction : Toward, to
Example of prepositions that shows time: Before, after