Vote up (and down)
Questions and answers can be vote up / down. Vote up grants reputation to the post author, this is a way to recognize the contribution done to the community. Vote down retire reputation poins, but less than the given by one Vote up. The idea of Votes up / down is to make that the best posts stand over other posts and give recognition to the posts author for their standing contributions.
Other contributions like editing posts also grant reputaion points.
The site keeps track of the reputation points earned by each user. The reputions points acculated are shown in the usercard and provide access to aditional privileges.
All the users start with the privilege to post questions, answers and post commments on their own posts. Once they earn reputation points they will be be unlocking privileges that will allow them to do more things in the site, like participate in Meta, which is a space to discuss the workings of Web Applications SE, participate in the site chatrooms among other things.
At higher reputation levels the privileges incluges access to moderation tools which allow the community members to collaborate in the moderation of Web Applications together with the community moderators.
The community moderators are community members that have assigned special privileges to help the community.