Install .deb

Packages are  manually  installed via the  dpkg  command (Debian Package Management System).  dpkg  is the backend to commands like  apt-get  and  aptitude , which in turn are the backend for GUI install apps like the Software Center and Synaptic. 
 Install a package: 
 To install a downloaded Debian ( Ubuntu ) package (.deb): Open Terminal and type 
 sudo dpkg -i DEB_PACKAGE 
 To remove a Debian (Ubuntu) package (.deb): 
 sudo dpkg -r PACKAGE_NAME 
 To Reconfigure/Repair an installed Debian (Ubuntu) package (.deb): 
 sudo dpkg-reconfigure packagename