Stack overflow is an web platform for users to ask and answer questions along with that every user has his/her own profile where they can up vote or down vote other users questions or answers.
Its an awesome community for the software developers where you get answers for about anything related to programming, if you are stuck at some point then you may seek for answers here.
As an stack over flow registered users you can also get reputation points which is really valuable in the world of software development, it very good thing to contribute to the open source community.