Here is a quick overview of some of the various apt-get commands to help you all along.
Contributers : Syngin, knute, and sharth.
This will install a package.
This will upgrade packages to the most recent versions. However, packages will not be updated with this command if it would require other packages to be either removed or installed.
This is quite simliar to apt-get upgrade, except that it will remove or install any programs needed to ensure that all packages are at the most recent version.
This will remove a package and leave it's configuration files.
apt-get --purge remove
Quite simply, this will do the same as apt-get remove , but it also deletes the configuration files as well.
This will search the descriptions of packages for the requested pattern.
This will show the description of the supplied package.
This will give information about a package, including configuration files, a description, dependencies, and other facts.
dpkg -S apt-file search
Will attempt to find out which package contains this file.
apt-file list dpkg -c
This will return a list of all files in this package.
This will attempt to run a command, most often "./configure", and attempt to download any packages that are needed to fill it's dependencies. It takes the dependency hunting out of building from source.
apt-get update apt-file update auto-apt update
This will update the package lists to the most recently available versions (within the selected repositories as seen in /etc/apt/sources.list).