The busy bloggers at LinuxHelp has made e nice overview of how to use apt-get/dpkg for the new users.
Read it here if you're new or need to check if you've forgotten something:
Debian is one of the earliest Linux distribution around. It caught the public's fancy because of the ease of installing and uninstalling applications on it. When many other linux distributions were bogged down in dependency hell, Debian users were shielded from these problems owing to Debian's superior package handling capablities using apt-get.