In addition to Edd’s great answer, I would point that:
The card which you have seen is the T-10 (http://www.tmb.cat/en/sistema-tarifari-integrat/-/ticket/T10), which costs €9.95 and is valid for 10 journeys on the metro, buses and trains, including up to two changes (eg train to metro to bus, or bus to metro, but not metro to metro). These are valid for more than one person to use simultaneously, as long as the group does not split up at any point. You can also get day travel passes for €8.40, valid for one person for as much travel as needed in one day, or, if you think you’re going to do a lot of travel, you can get a T-70/30 (http://www.tmb.cat/en/sistema-tarifari-integrat/-/ticket/T70-30) which is valid for 70 journeys (with changes, as per the T-10) in 30 days, for €59.50 (the T-50/30 is only valid for one person to use at once while the T70/30 can be used by more than one person simultaneously). The T70/30 might be the best solution for you as it would let your group do 14 journeys for the cost of two five day passes. The T-70/30 is also valid to and from the airport on metro line L9Sud, which the T-10 doesn’t cover.
If you have a Euro<26 card, you can get a 20% discount on regional train fares (this includes the Avant trains to Figueres). The card issued in Catalonia looks like https://www.carnetjove.cat/bundles/undfmain/images/img26.jpg?v1.3.8, but the important thing is the “EC” logo. If you don’t have one then unfortunately there are no discounts for being under 26, and adult fares are payable from age 15 up. If you read Spanish, more information on this is at http://www.renfe.com/viajeros/tarifas/carnet_joven.html. Alternatively, you may be able to get cheaper fares on long-distance trains at the Renfe website (for Tarragona, make sure you don’t book to Camp de Tarragona, which is the high speed station but is around 12km outside Tarragona itself).
Credit:stackoverflow.com‘