A preposition is a word placed before a noun or noun-equivalent to show in what relation the person or thing denotes and thereby stands to something else. (- J.C. Nesfield)
A preposition is a word with a noun or a pronoun to show how the person or thing denoted by the noun or pronoun stands in relation to something else. (-Wren & Martin)
How many Kinds of Prepositions
Simple Preposition: in, before, of, to, at, by, without, from, outside, beside, on, with, for, after, above, over, between, among, alone, about, within, off, since, beyond, toward/towards, around, behind, beneath, besides, despite, down, during, except, near, onto, past, through, till, under, underneath, until, up, upon etc.
Double Preposition: into, onto, within, without, from, among, towards etc.
Compound Preposition: across = on + cross, along = on + long, behind = by + hind, beneath = by + neath, beside =by + side, underneath = under + neath etc.