To create a new user, first login as yourself.
Then from the Leaf > Applications > System Tools > UXterm run the following command:
sudo adduser <new_user>
Where <new_user> is the login name for the new user . You may be prompted for your password.
Dialog on terminal when I added a user named 'onemore':
root@gPC:~# adduser onemore
Adding user `onemore' ...
Adding new group `onemore' (1004) ...
Adding new user `onemore' (1004) with group `onemore' ...
Creating home directory `/home/onemore' ...
Copying files from `/etc/skel' ...
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Changing the user information for onemore Enter the new value, or press ENTER for the default
Full Name []: Room Number []: Work Phone []: Home Phone []: Other []:
Is the information correct? [y/N] y
root@gPC:~#
For a better, long-term way, see users