Quick Usage:

apt-cache to search the local database for available packages.

apt-cache search [search terms] will find packages that sound like what you want and:

1. apt-cache show [packagename] will return more details on a particular package.
2. apt-cache showpkg [packagename] will return more details on a particular package.
3. apt-cache policy [packagename] will return which versions are available along with the priority of each version.

apt-setup will enable you to change mirrors. The alternative is to edit /etc/apt/sources.list manually (which I prefer).

apt-get clean clears the local repository of all retrieved package files.

apt-get autoclean clears the local repository of retrieved package files of programs that are no longer installed.

dpkg -l [packagename] will list the version and a short description of the package we have installed.