In the Accomodation page (when available) you can see how to go from the hotel to the university, and viceversa (just apply the inverse).
How to arrive from the airport: There are direct buses every 5-10 minutes going back and forth from the center of Barcelona (Pl. Catalunya and Pl. Universitat) to the airport BARCELONA-EL PRAT and viceversa. Each trip costs 5.90 euros and it is about 30 minutes long (depending on traffic). All information can be found here.
We notice that from Terminal 2 there is also the train station (RENFE) with trains going to Sants and Passeig de Gracia; the later being quite close to the center. In general, though, the bus is a more direct option.