Add a standard user in Kali Linux,ubuntu Mint.

Anyone who uses computer is called user.You can add as many as users you want in Linux. There are two types of users in Linux.

Root user

Root is the most powerful user.Root has access to all the files. Root can delete,modify,change file permissions and install and uninstall programs in linux.By default root can access all the commands. Root is also known as the Superuser in Linux.

Standard user

Standard Users have limited access to computer.Standard users does not have permission to delete,modify,install and uninstall programs.So non root users can not perform administrative tasks.It's too dangerous to run root user you may delete system files accidentally without even knowing. Specially in kali Linux 2.0 by default it operates with root user, but in most Linux distro's you have to access root with sudo.So it's safe to have a non root user specially in kali. So let's create a standard user.Open your Terminal and type the following command:

sunny@zeeroseven:~$ useradd user1 -m -s /bin/bash -g users

Now check if user is created or not.Type the following command:

sunny@zeeroseven:~$ ls /home
sunny  user1

As you can can see we have created new user user1 successfully.This is where -m comes into action. it tells linux to have home a directory for user user1. Now that we have created new user but it doest not have it's own password.So let's assign a password to user1 with the following command.

sunny@zeeroseven:~$ passwd user1
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully
sunny  user1

When you type passwd user1 command you will be asked to enter new password and re-enter again for confirmation.That's it we have created user1 with the password. If you dont supply any user name with the command passwd then your root password will be changed.
Now you can login with user1 just type:

sunny@zeeroseven:~$ login user1
Last login: Thu Oct  8 06:24:46 EDT 2015 on pts/0
Linux zeeroseven 3.18.0-kali3-amd64 #1 SMP Debian 3.18.6-1~kali2 (2015-03-02) x86_64

The programs included with the Kali GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Kali GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.

Delete User

userdel command delete users on linux.type the following command:

sunny@zeeroseven:~$ userdel user1

if you type ls /home you will see that user1 is still there.That's because it has deleted user from the system but did not delete it's home directory. Remove user's home directory with:

sunny@zeeroseven:~$ userdel -r user1