In this tutorial the instructor shows how to compute the Surface Area of a Cone. He explains that you need to find the individual surfaces areas first. Hence the bottom part of the cone which is circular can be calculated as Pi*r*r, where r is the radius of the base circle. Now for the sides surface of the cone, it looks like a sector and he derives its area thorough some deduction. Now he adds both the base surface area of the cone, and the lateral surface of the cone which finally gives the surface area of the cone. If you want to compute the surface area of a cone follow the instruction given in this video tutorial.