Railpass Europe

Please help with rail pass info!?
I don’t understand how the railpass quite works. Do you have to pay to make a reservation even though you have a pass? Please read the reservatons and overnight train section under this web page & explaine how it works! Have you ever traveld in Europe on a rail pass, how did it work?
http://www.raileurope.com/us/common/how_pass_works.htm
You are not required to have a reservation for a seat but if you do not have one, you may end up standing on the train. I travelled Eurail in Italy and I recommend getting a reservation and upgrading to first class.