If it's a rectangular prism, these are the steps:
Find the area of two sides (Length*Height)*2 sides
Find the area of adjacent sides (Width*Height)*2 sides
Find the area of ends (Length*Width)*2 ends
Add the three areas together to find the surface area Example: The surface area of a rectangular prism 5 cm long, 3 cm. wide and 2 cm. high = 5*2*2 + 3*2*2 + 5*3*2 = 20 + 12 + 30 = 62 cm2.