Adding and Removing User in Ubuntu

 First login to root:

..$ su
..root# adduser fly
Adding user `fly' ...
Adding new group `fly' (1001) ...
Adding new user `fly' (1001) with group `fly' ...
Creating home directory `/home/fly' ...
Copying files from `/etc/skel' ...
Enter new UNIX password:

Retype new UNIX password: 

passwd: password updated successfully

Changing the user information for fly

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#

After adding user fly we can add it to the sudo group:

..root# usermod -aG sudo fly

..root#

Now we should switch the fly:

..root# su - fly

..fly$

If you want to delete it

Close and reopen the terminal

Login as a root:

..root# userdel -r fly