About 3 years ago we docked in Barcelona and had a hotel near the Ramblas reserved for us. We picked up a taxi at the port--he drove us to the hotel--he waited while we left our luggage--then he drove us to Sagrada Familia. I think we gave him about 25 €. On another occasion we paid 15€ (with tip) from a taxi stand by our off-Ramblas hotel to dock. Taxis in Barcelona are pretty easily available at the Taxi stops.
We are probably older than you are--so I think you could manage a taxi transaction in Barcelona. haha.