At login time, you'll see a prompt resembling the following on your screen:
Here, enter your username, and press the Return key. Our hero, larry, would type the following:
Now, enter your password. It won't be echoed to the screen when you login, so type carefully. If you mistype your password, you'll see the message
and you'll have to try again.
Once you have correctly entered the username and password, you are officially logged into the system, and are free to roam.