Also, i am very confused with how it works, do i have to prebook every time i want to go somewhere or can i book a train on the day i need it. Is it possible to get a train from paris to pescara?
You can travel by bus super cheap in parts of Europe. I went from Riga, Latvia to Warsaw, Poland, 1 15-hour trip for under $20US.
Check out companies like EuroLines, EcoLines, Orange, etc.
For your train questions there is a great amount of information at Seat61.com. about 6 years ago
Price wise no, flying is cheaper but the benefit of trains is that you depart/arrive to city centers. Be careful when you select your package regardless if you are or not visiting a country you should count it if the train crosses it, about 6 years ago