The main means that people use to install packages on their system is via a program called apt-get, from the apt package. Note that the actual program that installs packages is called dpkg. However, this program is more of a low-level tool. apt-get is a higher-level tool as it will invoke dpkg as appropriate and also because it knows to install other packages which are required for the package you're trying to install, as well as how to retrieve the package from your CD, the network, or wherever. Other front-ends for package management, like aptitude and synaptic are also in use and depend on apt-get. These front-ends are recommended for new users, since they integrate some additional features (package searching and status checks) in a nice user interface. apt must be configured so that it knows where to retrieve packages from. The installer largely takes care of this automatically based on what it knows about your installation medium. The results of this configuration are written to the file /etc/apt/sources.list, and you can examine and edit it to your liking after the install is complete.