what is a preposition?

Answer 1

You can find the definition here.

http://dictionary.reference.com/browse/preposition

However, I've always had difficulty understanding that definition. The best way to learn prepositions is to memorize the common ones.

http://grammar.ccc.commnet.edu/grammar/preposition_list.htm

Also, I recommend you learn to recognize prepositional phrases.

http://grammar.uoregon.edu/phrases/prepositionalP.html