You can vote up an answer awarding that person 3 credits and 1 for yourself if you agree with and like what the person has said. Some people do it to help each other get more credits to advance to the next level. There is also the vote down button which I guess is used if you do not like a response to a question. I am not exactly sure if that person loses credits or what because I have never used it. Hope that helps. Have a great weekend.