random question

Ok so I'm not sure where I should post this to find out or if I just missed it in the FAQ but how do I gain lvls on my profile.. like for example mine has a big 0 with a circle around it but I've seen others with higher numbers.. I was just wondering how to make it go up and what the number ultimately means ..again if this was in the FAQ I apologise and also not know where I should ask this question.