You are probably familiar with:
apt-get install <package-name>
command to install new packages to your debian based distro.
You can easily search for a package from command line with the following command:
apt-cache search <package-name>
if you are not completely know package name get little help from grep and pipe (|) combinations. For example if you want to install setup-tools package for python then search can be:
apt-cache search python | grep setup
Then you can install the package.