User information for Unix machines is stored in a file called /etc/passwd. By default, your system will allow any valid Athena user to log in when physically at your machine, but only users in this file to log in remotely (i.e., by telnet or rlogin). In order to allow users the ability to log in remotely, you need to put them in the passwd file.
To do this, you need to become root and run
/bin/athena/hesinfo user passwd >> /etc/passwd.local
This will append the appropriate user information to the file. Note
that by default even you aren't in the file, so you'll probably want
to add yourself ASAP.
/bin/athena/hesinfo user passwd >> /etc/passwd
You may be wondering why you should change /etc/passwd.local in addition to /etc/passwd. The reason is simple: Any changes you make only to /etc/passwd will be lost because /etc/passwd.local is copied to /etc/passwd every time you boot your machine. (There are several reasons for this, such as that it keeps /etc/passwd from growing too large and allows for improved security.) The same applies to /etc/group and /etc/group.local.
If you wish to restrict access of users of the machine to just those in the password database, edit the file /etc/athena/rc.conf and change the line NOCREATE=false to NOCREATE=true. Then run touch /etc/nocreate. This will only allow users in /etc/passwd.local to log in to the machine whether they try to log in remotely or at the console. If you want to change this back, remove /etc/nocreate and change /etc/athena/rc.conf to say NOCREATE=false instead of NOCREATE=true.
At the other extreme, it is also possible to let everybody log in to your machine remotely. If you really want to do this, set NOREMOTE to false in /etc/athena/rc.conf and rm /etc/noremote. Note that if NOREMOTE is set, people can still log in at the console; if you don't want them to be able to do so, set NOCREATE.
A third flag you may want to know about is NOATTACH, which is set and unset the same way as the other two flags. If it is set, home directories will not be attached.