How to add new user in Ubuntu

Open Settings .
Click on Details from the menu at the bottom left .
Click Users.
Click Unlock at the top right of the screen.
Enter your password to authenticate to the system.

Your account must have admin privilege for this to work
Click on the Add User button at the top right that has just appeared.
Fill in the details of the user to be created. Choose whether you want the user to be normal user or administrator.
Select Set a password now, enter a complex-enough password till the Add button ad the top right is enabled / turned green and click on the Add button.
Your new user should now be added and listed among the other users in the system.