I'll give you two answers, since I'm not really sure what this is asking.
πr2 is the formula for the area of a circle.
Here is an example of how to use the formula:
Say that you round π to 3.14 (that's usually how you round π). Also, say r, or the radius (half of the diameter, and the diameter is a line that passes through the center of a circle) is 4.
42 really means to multiply 4 by itself, 4. Anything with 2 means to multiply it by itself once. Back to our example, 4*4 is 16.
When you see the π and r together (πr) like that, it means to multiply them together. In our example, 16*3.14 is 50.24.
And there you have it. That's all you do to use the formula.
Hope this helped.
