they are important tools for creating variety and meaning in description
they are words used to describe a relationship between two or more things
they can be a spatial relationship (her bag was under the chair)
a time relationship (they arrived on Monday)
a manner in which something is done (they went by car)
prepositions allow the reader to navigate your scene. They help build connections between the things and the scene. they develop a 3D impression of your scene in the readers mind.
On the brilliant blue chair sat the girl, mind deep in the book. Above the girl, towers of books stacked up towards the sky. On and on the books continued into the distance, creating a magnificent world. Through the sky, the delicate pages ruffled in the wind as the words danced along the page.