Install a package:
sudo apt-get install <packagename>
Remove/uninstall a package:
sudo apt-get remove <packagename>
Update local package index:
sudo apt-get update
Comment: Package index is database of available packages from the repositories defined in the /etc/apt/sources.list
Remove PPA:
sudo add-apt-repository --remove http://whatever/ppa
Thanks to: http://askubuntu.com/questions/307/how-can-ppas-be-removed
Thanks to: https://help.ubuntu.com/lts/serverguide/apt-get.html