how to enable the non-free archive repos or Universe and Multiverse repos for Ubuntu

ONE option available for newer releases of Ubuntu:

$ sudo su
$ apt-add-repository multiverse && apt-add-repository universe && apt-add-repository restricted && apt-get update

And some other way! --> Examples:
  apt-add-repository 'deb http://myserver/path/to/repo stable myrepo'
  apt-add-repository 'http://myserver/path/to/repo myrepo'
  apt-add-repository 'https://packages.medibuntu.org free non-free'
  apt-add-repository http://extras.ubuntu.com/ubuntu
  apt-add-repository ppa:user/repository
  apt-add-repository multiverse
  
## After adding the repos remember to check if the repos are activated:
## Run in terminal:
$ grep ^deb /etc/apt/sources.list

## To Remove A repository; Simply add ' -r ' the the commandline script
## by inserting it directly after 'apt-add-repository'.
## i.e: 
$ apt-add-repository -r multiverse && apt-get update