User rating is how our users rate you. If you make a good post then someone may press the applause button next to your name and hey presto +1 to your rating. It also works the other way around if you press boo. You get nothing for your user rating but the higher it is the better you can feel about yourself
You can't change your own rating and you have to have over 5 posts to change someone elses rating. Work out for yourself why your rating is at -2.