Naturally Grammar
What is a Preposition?
Any member of a class of words found in many languages that are used before nouns or pronouns

What Does a Preposition Look Like?
Above, between, under

Mnemonics & More
Where something is; How are two things related

Preposition:  A Few Examples
Under, above, between, inside, outside, beneath, on, top, beside, underneath, on


What Is a Pronoun?
Any member of a small class of words found in many languages that are used as replacements for nouns

What Does a Pronoun Look Like?
He, you, she

Mnemonics & More 
Talking about a noun without using its name

Pronouns: A Few Examples
I, you, he, she, it, we, you, they, me, him