Adding Additional Users
Some computer systems end up being used by only one person, but many are shared among several people. When more than one person uses a computer system, it is always a good idea to create a unique account on the system for each person. This also gives everyone who uses the system the freedom to customize their experience without affecting the experience of other users (e.g., each user may choose her own desktop wallpaper or theme and it won't change the preferences of others). This also means that you may create accounts with administrative privileges for people you trust to make changes to the entire system and less privileged accounts for people who do not need this power. This keeps your system more secure.
To add additional users, select System > Administration > Users and Groups. In the box that appears, click the Add button in the lower left corner. In the Create New User dialog box, enter the new user's name and a short name the user will use to login (e.g., Matthew Helmke and matt). You may also choose to have this user's /home folder encrypted as it is created. After you click OK, you will have a chance to enter a password for this user or to generate a random password.
You can even click the option to not ask for a password from this user when he logs in, but we don't recommend that unless this is going to be an account without administrative privileges and will be the default for booting in a very special case, such as a computer used primarily by children with a limited account but with an administrative account used by an adult for occasional maintenance.
Once you click OK on the password box, the account will be created and listed in the Users Settings window. By default, the account created is that of a normal user. If you want to give this new user the ability to administer the system, or other privileges, highlight the user's name in the list on the left and then click Advanced Settings at the bottom right. You can change the user's contact information, privileges, and more from here.
You may also delete users, change and manage user groups and memberships, and more from this location.
If you would prefer to do this from the terminal, use the adduser command while logged in to an account with administrative privileges:
matt@laptop:~$ sudo adduser corey
After you enter your password, this will add a new user named corey. You will be asked several questions in the process. Answer them, and at the end, the account will be created.
To delete a user from the command line, use the deluser command in place of adduser in the above example. You can learn more about dealing with users from the command line in the appendix.