The surface area is found by finding the area of all shapes creating the surface, and then adding them together.
Example:
If we have a 5 x 5 x 5 cube, we will find all six sides. Since 5 x 5 is 25, and 25 x 6 = 150, the surface area of this example cube will be 150 units².
Why the x 6? Since it is a cube all the sides have the same area, and a cube has 6 sides.