At login time, you'll see a prompt resembling the following on your screen:
mousehouse login:
Here, enter your username, and press the 
key. Our
hero, larry, would type the following:
mousehouse login: larry
Password:
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
Login incorrect
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.