How do you find the are of the circle and the square

You don't have enough math yet to be able to derive the formulas,
so you just have to memorize them:

         Area of a circle = (pi) x (radius of the circle)²

         Area of a square = (the length of one side of it)²

You may think you can't memorize them, but that'sexactly
what homework is for.

Take ten circles of different sizes and find the area of each one.
Then take ten squares of different sizes and find the area of each one.

You'll remember the formulas for the rest of your life.  I guarantee it.

In fact, I'd be very surprised if you're in high school math now and you haven't
already done this for homework. 

Let me rephrase that:   I'd be very surprised if you're in high school math now
and this hasn't already been assigned as homework.