In grammar, a preposition is a part of speech that introduces a
prepositional phrase, a group of words that modify a noun or verb
by using a noun, pronoun, or gerund (the object of the
preposition). In "the man with the car" the word car is used to
further specify which man is being addressed. In "he talked about
what we should do" the object of the preposition "about" is the
entire clause "what we should do."
Some common prepositions are:
about, above, across, after, against, among, around, as, at,
before, behind, below, beneath, beside, besides, by, down, during,
for, from, in, inside, into, near, of, off,on, out, outside, over,
through, to, up, under, with, without and but.