Dpkg

dpkg is a tool to build, install, remove and manage packages in Debian. It is called by apt-get to actually install the packages after apt-get has resolved dependencies and downloaded packages.

dpkg is a useful tool to find out information about individual packages:
 * to see which packages are installed: dpkg -l
 * to look at a package description: dpkg -I PackageFile.deb
 * to look at package contents: dpkg -L Package
 * to search for a filename within installed packages: dpkg -S SearchTerm (to also search in not installed packages you can use apt-file).
 * to (download and) install packages:dpkg -i *.deb
 * to find what package provides the installed file /bin/ls: dpkg --search /bin/ls
 * to find what program provides the file Xlib.h:auto-apt search Xlib.h

= See also =
 * Rosetta stone for rpm vs dpkg - If you understand rpm or dpkg and want to learn the other