I want to know...

I want to know what is rating and what is contribution????? And what does it mean----Rating: 1255 Contribution: -34...... And also I have participied in CODERSTRIKE raund 1. and I solved 2 problems at that contest. before the contest my rating was 1285 after that contest My rating became 1255. DId my rating get worse? WHY??????

can anyone explain me how to calculate codeforces rating?

can anyone expalin me why I cannot see me rating? I cannot find my rating anywhere.. w