The web application you are using right now is called Confluence. Confluence is an example of a wiki, a kind of web application designed to encourage easy editing, documentation, and collaboration. Wiki means "fast" in Hawaiian.
There are many different wiki applications for different purposes. For example, Wikipedia uses the MediaWiki software, which is designed to allow completely public editing. In contrast, Confluence is set up for corporate use. It is simple, easy to use, and allows fine-grained access control.
Follow this quick tutorial, and soon you'll be using this wiki like a pro.