Open Directory Utility located in Application→Utilities. You may have to unlock Directory Utility to make changes. Once it's unlocked, go to Edit→Enable Root User, and then type in a password for your root user. The root user is activated now and the Other Users option shows up on the login window.

To enable sudo for a user> Log in a user with admin rights. Open terminal. Become root with su -. Edit sudoers list to add other users using the command visudo.