What is a preposition?
A preposition is a set of words used in close in connection with, and before nouns and pronouns to show their relation to another part of a clause. For more information go to http://encarta.msn.com/dictionary_1861737212/preposition.html. Another good website is http://grammar.about.com/od/pq/g/prepositerm.htm or http://www.advanced-english-grammar.com/list-of-prepositional-phrases.html.