Evolution is not your typical Linux application in that there are no official binary packages available for download. From the official site you can only download the source packages, which must be compiled. That is not so much of a problem with Evolution because it is now automatically installed with the GNOME desktop. You can also install Evolution with your package management system. Of course there are two ways to install with a package management system: GUI or command line. If you decide to install via command line it will look something like this (depending upon your distribution):
urpmi evolution
sudo apt-get install evolution
yum install evolution
From the GUI package management system (such as Synaptic, Yumex, or Rpmdrake) you would simply search for Evolution, select it for installation, and apply the changes.
Once Evolution is installed you will find it, most likely, in the Internet or Networking sub directory of your main menu.