Twitter

Twitter is a miniblog and getting to be one of the most popular SN sites. A good number of people do not tweet themselves very often, but rather they follow celebrities, news, information, etc.
Some college students use it for group  work and note taking or note sharing.
Some people just twitter inanely. High school students often gossip on it or some even share answers with it comfortably out of sight on their phones. Many companies and organizations use it for PR and advertising. Others just use it to keep up with what is current (most twetted topic). It has been useful to get news out of Iran and other places along with other SN sites.

As with other texting there is a whole new abbreviated vocabulary:  
8:] a Gorilla
and smilies


You will notice that many tweets contain links to other sites and are sort of bookmarks.

Twitter has many apps that expand it beyond just a miniblog. See the post below.

Help with Twitter

Mashable has a very comprehensive online Guide to Twitter.