Type whatever you want on your signature in this box. Finger people online and change your own finger information. At a minimum, this profile contains your real name, username, home directory, when you last logged in to the MHC system, and where you logged in from. You can also write a plan and check out other people's plans, see step 4 below. Any other user can look up this info about you, and you can look it up about anyone else.
Some people get quite creative.
Write a plan and check other people's plans. Talk to people. A split window will appear, and the computer will attempt to contact the other person. Wait until a connection is established and can start chatting with them, or until you give up on waiting for them to answer. Write a webpage.