Surface area is the total area of all the outside surfaces of a 3D shape. It is measured in square units such as $c{m}^2$ or $m^2$.

For flat-faced solids, add the areas of every face. For shapes like cylinders, include the curved surface as well as the flat ends.

The 2D area facts you need most are rectangle area $lw$, triangle area $A=\frac{1}{2}bh$, and trapezium area $A=\frac{1}{2}(a+b)h$. The height in triangle and trapezium formulas must be perpendicular to the base.