Joining a community

Joining a community.  What's it all about?  It's usually more formally called an "intentional community"; but what does that mean?  Let's roll this back to the more general, the inherent need for basic community, for all human beings (if indeed it is a need, a required-necessity).
Community also semantically seems to be a word comprised of two words: common and unity. What do we have in common which unifies us as a group? The academic etymology would be important to touch upon.  Let's start with the popular wikipedia source, although not to rest on its purported authority.  "A community is a small or large social unit (a group of living things) who have something in common, such as norms, religion, values, or identity. (and) ...a community is a group of people living near one another who interact socially."