I'm preparing for a vector calculus course in the fall and I've been self studying some topics. I've taken multivariable calculus and I'm familiar with using double integrals, how to solve them and how to use them to find volume. From what I've read so far, I'm familiar with how to SOLVE a surface integral by projecting the surface onto the xy plane. This just turns it into a double integral right? And what does the double integral of this projection give you (surface area????)? I'm just trying to figure out the PURPOSE of surface integrals and how they differ from double integrals. Sorry if my question is silly, but I haven't taken vector calculus yet and I'm trying to get ready.