A pronoun is a word used to take the place of a noun, which can be a person, place, animal, or thing. We use a pronoun to avoid repeating a noun that has already been mentioned. A pronoun usually comes after the noun it replaces.
Jim has a toothbrush. He uses it every day.
He and it in the second sentence are pronouns used to replace Jim and toothbrush: He is for Jim and it is for toothbrush. By using pronouns, we don’t have to write or say Jim and toothbrush again.
A pronoun may come before a noun that it replaces. In such an order, it has to be made clear so that a reader or listener knows which noun the pronoun takes the place of.
She, Jenny, is my only sister.
(She is a pronoun that replaces the noun Jenny, which in fact is an appositive.)
The only millionaire in the village, he is also the oldest.
There are different types of pronouns:
How to identify a pronoun in a sentence
A pronoun can also be a determiner, so how can we tell whether it is a pronoun or a determiner? It all depends on how it is used. As a pronoun, it is used independently, that is on its own without a noun following it.