Trip to Europe...Please Help!?

So i am planning a trip to Rome, Paris and Madrid the summer after i graduate from college kinda like a European tour. Anyway the trip is not for another year and a half but i am so excited. My question is how do i start planning and basically how should i prepare myself. I plan to stay in each city for approximately 10 days each. I've never been out of the country or flown on a plane so this is a new experience for me so i need this to be as simple as possible. Kinda like traveling for dummies lol. Anyway like i said before it will be during the summer maybe july-august so its gonna be for a month. i just need the basic questions to ask my self and approximate cost and i also want to travel by train when i go from one city to another at least once. anything will be helpful. Thank You All for your imput. Also websites and blogs about it would be helpful.