Well, the first question is, do you know how to use the Debian package management system to install packages?
What version of Debian are you using? Sarge, Sid, Woody.....?
If you have the Synaptic Package Manager installed, it is available.
Are you currently connected to the internet?
Let us know what the status of your usage of Debian is and we can guide you through the process. Quagga is in the Debian repository, so probably the easiest things to do is install it through Synaptic, or get into a terminal window, as root user and type in;
apt-get update
Then when the package repository is updated, type in;
apt-get install quagga