Well, you need an SSH client on your machine, and an SSH server running on the machine you want to log into. Start your SSH client, tell it to connect to the server, when you get a login request, log in with the username and password you have on the other machine and away you go.
What the exact process is depends on which implementation of SSH you use (Linux boxen probably have ssh installed already, I'm sure there are Windows implementations out there). Check the documentation (wherever it is for whichever implementation you choose) for precise instructions on how to use it, and might I recommend using the SSH v.2 protocol instead of v.1.
