Some more useful user-management commands (also limited to local users):

To add a new user you can use:

sudo adduser new_username

or:

sudo useradd new_username

See also: What is the difference between adduser and useradd?

To remove/delete a user, first you can use:

sudo userdel username

Then you may want to delete the home directory for the deleted user account :

sudo rm -r /home/username

^{(Please use with caution the above command!)}

To modify the username of a user:

usermod -l new_username old_username

To change the password for a user:

sudo passwd username

To change the shell for a user:

sudo chsh username

To change the details for a user (for example real name):

sudo chfn username

And, of course, see also: man adduser, man useradd, man userdel… and so on.

To add a user to the sudo group:

usermod -aG sudo username

Source: A command to list all users? And how to add, delete, modify users? – Ask Ubuntu