Barcelona has ONE airport (don't let any airline tell you different!).  It's called El Prat and has the code BCN.  It's located to the southwest of the city centre and, depending on where you want to go and the mode of transport you choose, is about 20-30 minutes from the middle of town.

If you are going straight from the airport to the stadium, you will want to take the no. 46 bus to Placa Espanya (this takes about 27 mins), and then the no. 50 to the stadium (10 mins).  Alternatively, you can take the Aerobus to Placa Espanya (see also Barcelona public transport).

If you are going from the airport straight into town, take the train (line 10) to Franca Station (or Sants Station).  Trains run every 30 minutes and the journey takes 32 mins to Franca Station, 17 to Sants.  Cost: €2.50.