Barcelona Airport Metro
The subway or “metro” has two stations in the airport. They are located at the exit of each terminal and are well marked. The metro departs every half hour and a ticket into the city costs 4.50 Euros.
You will buy your ticket in the station in one of the vending machines or ATMS. You can also buy the Hola BCN public transport card online that can be used for all of your city metro travel. This is a great idea if you will be in the city for a while. It offers multiple options for unlimited travel in the city.
The line is called L9 Sud and runs directly from Barcelona Airport to the South Entrance at Fira Gran Via (host of big venues like Mobile World Congress) but it is not super convenient for many travelers as it does not connect directly to the city center. You will have to transfer to another line at either Torrassa (L1) or Collblanc (L5) to get to your final destination.