Prepositions express relationships between words and link words together. They most commonly come before nouns or noun phrases. This document defines and provides examples for many common English prepositions such as at, in, on, under, over, beside, of, with, for, from, and to. It explains how each preposition indicates spatial, temporal, or other relationships. The document also lists five types of prepositions and some basic rules for using prepositions properly in sentences.