Facebook Chat is Facebook's answer to instant messaging. IM, or chat on Facebook, is really quite easy. All you need to chat on Facebook is a Facebook account, nothing to download or install.
When you log into Facebook you're automatically logged into Facebook Chat so you can chat on Facebook. Just go to your Facebook page and you can start to chat on Facebook right away.
At the bottom of every Facebook page you'll see your Facebook Chat tools. The first of the three Facebook Chat tools is the online friends tool. This simply tells you which of your Facebook friends is online right now. The next Facebook Chat tool is notifications which will let you know if you have any new Facebook notifications right from the tool. The third tool in Facebook Chat is the actual chat tool.