1- What is a preposition?

A preposition usually indicates the temporal, spatial or logical relationship of its object to the rest of the sentence.

E.g:We swimming in the pool.

2- What is a postposition?

Postpositions are something like English prepositions and include words like "among," "for," "to," and "with."

There are two types of Postpositions:

•Postpositions following a noun. Postpositions may be connected to the noun as a suffix or written as one word.
•Postpositions following a pronoun. Postpositions are connected to the pronoun and are said and written as one word.