My scope has a 2800mm focal length. I know its a good scope . . .?

so can you explain how it works (without aberration)? I just don't really get it. Its a Celestron CPC 1100. Also tell me how to figure magnification please! I always forget! Also, I just bought a 2" adapter and a low power eyepiece. What reasonably priced higher power eyepiece do you recommend? Thanks a bunch!!!!