Red Hat Linux
There are two ways that you can add users to your system: using the command line and the graphical tool.
To add a user from the command line, open up a terminal and switch to the root account by issuing the su command and typing the root password. Then use the command useradd followed by a space and the username as the argument.
For example, if you want to add me to your system with the username tolgabalci, then the command will be useradd tolgabalci
After you issue the command, you will be prompted to enter the user’s password twice. When done, your user is added to the system, with their /home directory and login shell defined.
The second option is using the graphical interface. You can either go to System Settings -> Users & Groups or open up a terminal, switch to root, and issue the redhat-config-users command. In both cases you will have the same configuration window.
In the window, click “Add User" in the top left and a dialog box will open to enter the username and password. The home directory of the user is created automatically and their default login shell is defined.