Installing K3B is simple. From the command line you can enter one of the following commands (depending upon your distribution):
sudo apt-get install k3b
urpmi k3b
yum install k3b
Or you can fire up your package management GUI, search for K3B, select the results, and click Apply. Once K3B is installed you will most likely find the menu entry in your Multimedia sub menu. Or you can always run K3B from the command line with the command k3b.