Buy Eurorail

Eurorail question….?
I will be traveling to Europe next summer and plan on visiting about 9 or 10 cities all over Europe in a 2 month span. I plan on getting the Eurorail pass, however, a friend said they think that I have to buy tickets in addition to the eurorail pass. If that is the case, is it even worth paying the 1000-1300 bucks for it?!?!?! On average, how much more will I have to pay? I’m still a little confused as to how it works exactly, so any advice would be much appreciated. Thanks in advance
If you travel with the fast trains you will need to buy supplements or pay for seat reservations. On most trains, specially the slower ones, you can travel for free.
http://www.raileurope.com/us/rail/passes/eurail_index.htm