Welcome to the wonderful world of geometry. Geometry takes the basic understanding of algebra and applies it to shapes and angles. Geometry also includes a study of right triangle trig that is developed through similarity relationships.
Basic area formulas:
Rectangle = bh
Triangle = 1/2bh
Circle = ∏(radius squared)
Perimeter formula:
Add all side lengths of the polygon
Circle - 2 ∏ (radius)