A preposition is a word that shows the relationship between a noun (or pronoun) and another word in a sentence. It often tells you about place, time, direction, cause, or manner.
Common examples of prepositions:
Place: in, on, at, under, between
Time: before, after, during, since
Direction: to, into, onto, from
Other relationships: with, about, for, of
Examples in sentences:
The book is on the table.
She arrived after lunch.
He walked to the park.
This gift is for you.
In each sentence, the preposition connects a noun or pronoun to the rest of the sentence and gives more detail about how they relate.