Trains in Spain are quite reliable, fast and very cheap! The main train station in Barcelona is Sants. You can get there via Metro line 3 and line 5. Most international trains leave from Sants and they have a local & tourist information centre.

The other station is Estacion de França. Some international trains go from here and you can get there via the metro on line 1. Sants is much bigger and thus will have far more international and national trains arriving and departing. Best bet is to check out the main train web site of Spain on www.renfe.es