Sentences can be written in the first, second or third person.
The first person uses the words I and we.
I love chocolate ice cream.
The second person uses the word you.
Do you love chocolate ice cream?
The third person uses the words he, she, it and they.
She loves chocolate ice cream but he doesn't.
When we change a sentence from the first person to the third person (or the other way round), we often need to change several words. Look at these two sentences:
I am wearing my new jacket.
He is wearing his new jacket.
You will see that I and my have changed to he and his, but the verb has changed as well, from am to is.