Let's begin with the basics of the verb TO BE:
Now as you can see we use AM only with "I." We use IS with "he," "she," and "it." Finally, we use ARE with "you," "we," and "they."
How about the negative forms of the verb TO BE?
Well, there are actually two forms of the negative in English with the verb TO BE, except in the first person singular:
You're not OR You aren't
He's not OR He isn't
She's not OR She isn't
It's not OR It isn't
We're not OR We aren't
They're not OR They aren't
The verb TO BE is the most important verb in any language, so it's very important to learn these conjugations. If you have trouble remembering them, write each form down 5 times in your notebook. You can do it!