Where can we get packages from?
Ubuntu stores all of its packages in locations called software channels or repositories. A software channel is simply a location which holds packages of similar types, which can be downloaded and installed using a package manager. A package manager will store an index of all of the packages available from a software channel. Sometimes it will 're-build' this index to make sure that it is up to date and knows which packages have been upgraded or added into the channel since it last checked.
There are four Ubuntu software channels for each architecture - Main, Restricted, Universe and Multiverse. Each has a different purpose. By default, only packages from Main and Restricted can be installed. If you would like to install packages from Universe or Multiverse, see the Repositories page for instructions on how to do this.
In addition to the official Ubuntu repositories, it is possible to use third party repositories. Be careful, though - some are not compatible with Ubuntu and using them may cause programs to stop working or may even cause serious damage to your installation. The page http://www.ubuntulinux.nl/source-o-matic (page removed - why) can help you to find extra repositories, and the Repositories page gives instructions on how to enable them.
Installing a Package: This section explains how to install packages using the various tools available in Ubuntu,Xubuntu,Edubuntu and Kubuntu.
