A pronoun is a word that stands in place of a noun.
Kayden lay down on the bed and in two minutes he was asleep.
In this example the pronoun 'he' is used instead of repeating the noun 'Kayden'. Words like I, he, she, it, we, you, they, him, her, us and them are personal pronouns. They are used instead of the names of people or things.
There is another type of pronoun called a possessive pronoun, which is used when something belongs to someone.
Kayden lay down on his bed.
In this example, the pronoun 'his' shows that the bed belongs to Kayden. (It would sound strange to say 'Kayden lay down on Kayden's bed.')
My, his, her, its, our, your and their are all possessive pronouns:
Laura ate her dinner.
The elephant lifted up a branch with its trunk.
The children finished their homework.