$ sudo apt-get update
$ sudo apt-get install quassel-qt4 

quassel-qt4 is installed in your system.

Make ensure the quassel-qt4 package were installed using the commands given below,

$ sudo dpkg-query -l | grep quassel-qt4 *

You will get with quassel-qt4 package name, version, architecture and description in a table

quassel-qt4 package basic information: