The triangles in the prism are congruent, so you find the area of one triangular base and multiply it by two.
Then, you find the area of each of the rectangles. This is a mandatory step unless the question specifies that the triangle bases are isosceles or equilateral. In those cases, you can multiply the rectangular face by two or three and find the other rectangular face. (if isosceles)
Just add up the areas of all the faces and that is the surface area of a triangular prism.
