Create a new user account on your GNU/Linux machine
Easy as pie. replace <username> with the login you want to create, then follow the instructions.
sudo adduser <username>
Maybe you need this new user or yourself to be in a specific group, in that case to add an existing user to an existing group:
sudo adduser <username> <groupname>
Note: creating a user is effective immediately but adding an existing user to a new group will only be effective if the added user fully log out and log back in from the console (in case the existing user is already loged in of course....)
questions? RTFM :D