A preposition is a word or group of words that gives information about where, when or how something takes place.
The boy was riding his bike beside the lake.
He always went for a bike ride after lunch.
Today he was alone but he usually went with his brother.
There are over a hundred prepositions in the English language. Here are a few of them:
at, during, on, with, under, over, by, in front of, behind, towards, among, before.