Understand how to form a prepositional phrase.

Prepositions generally introduce prepositional phrases. Prepositional phrases look like this:

preposition + optional modifiers

+ oun, pronoun, or gerund

Here are some examples:

At school

At = preposition; school = noun.

According to us 

According to = preposition; us = pronoun. 

By chewing

By = preposition; chewing = gerund. 

Under the stove

Under = preposition; the = modifier; stove = noun. 

In the crumb-filled, rumpled sheets

In = preposition; the, crumb-filled, rumpled = modifiers; sheets = noun.