[HELP]Evaluating the performance of a computer system?

So yeah, title says all, this is part of my assignment work and I've been struggling to get my head around it for a few days, I have downloaded a benchmarking utility and that can break down the areas for the performance e.g. CPU, Memory, GPU, I can't think of anymore performance factors that would affect a computer system and I'm unsure how I can justify the procedures, can anyone guide me to any links that might make a little more sense? I understand the meaning of performance, but i'm new to the hardware side of computers so i'm a little unfamiliar with a few performance factors, any sources of advice would be kindly appreciated, thanks