This is out of date, the "User Accounts" app has changed in Ubuntu 11.10 and no longer has many functions.
See the official Ubuntu Desktop Guide for up-to-date instructions on adding new users.
For Kubuntu, see the Kubuntu Desktop Guide.
When Ubuntu and/or Kubuntu are initially installed, a single user account was created. It is possible to create additional user logins on your system.
There is more than one way to add a user, however this wiki page will briefly discuss the easiest and most common ways. The two ways shown are:
Command-line - adduser
Graphical is the easiest solution, while the command-line offers the possibilities of multiple tasks at one time.
Location: System > Administration > Users and Groups
NOTE: In the default installation of Ubuntu 9.10 'Karmic Koala', the + Add User button will be grayed out, and a Click to make changes button with a picture of keys will be an the bottom of the window. Click that and enter the sudo password to make the + Add User button active.
Press + Add User, this will open up the User Account Editor. The minimum requirements are Username and password. For the Username, do not use spaces, and do use ASCII characters. On the User privileges tab, add privileges that the new user will have access to, such as use audio devices.
Location: Kmenu > System Settings > Users & Groups
Press Administrator Mode, this will pop up a password box. Enter your password. Press New..., this will open up the User Account - KDE Control Module. The minimum requirements are Username and password. For the Username, do not use spaces, and do use ASCII characters. On the Secondary Groups area, press Select..., and add priviledges that the new user will have access to.
To add a user you must use the sudo command (for an explanation of what that means, see the RootSudo page). Here are the commands:
To add a user. NOTE: do not use the useradd command.
$ sudo adduser <username>
To see the options for adding a user try the man command.
$ man adduser
Here is a useful example of the useradd command. Why use useradd? It gives a few more options for special cases. To add a user, give her a standard home directory in the /home folder and specify the shell she accesses by default do this:
$ sudo useradd username -m -s /bin/bash $ sudo passwd username
You might also wish to create a new group for your users.
# sudo addgroup <groupname>
To add a new user to a existing group you would do this:
# sudo adduser <username> audio
To add an existing user to an existing group you can use the same command:
# sudo adduser <username> <groupname>
# sudo usermod -aG <groupname> <username>