You should be able to draw a triangle, a rectangle, a 5-sided figure,
and a 6-sided figure (like a STOP sign). Maybe you can even
draw shapes with more than 6 sides. (The sides don't have to
be equal lengths.)
In each one, count the sides and count the angles. In each of your
drawings, you'll find that there are the same number of sides as angles.
You'll start to suspect that maybe this is true no matter how many sides
the polygon may have.
Yes. It's true.