The Metro rail system is a fantastic way to get around Barcelona, especially if you are a tourist and are unsure how to communicate with taxi drivers, bus drivers, and so forth. The Metro system is very similar to the sort of systems you see in European countries; there is nothing new or scary about the Spanish Metro system. Most Metro trains only wait for two minutes in the station before moving on, they are fairly well organized, which means delays rarely extend for longer than ten minutes.
Buying individual tickets for each trip is okay if you are travelling without a specific touring plans, but if you want to save money, you should probably buy a travel card. There is the T10 card that entitles you to ten Metro trips, and there is the Barcelona Tourist Travel pass that gives you unlimited Metro travel between 05:00 and 23:00 for 3, 4 or 5 days. There is also the Barcelona Card that gives you unlimited travel options and discounts on local attractions.
The T10 cards offer you ten trips on Metro trains and/or buses, but there are restrictions. For example, you can use some of the TBM night buses and TMB air buses, plus the RENFE train, but not the airport metro stops Aeroport T2 or Aeroport T1, or the Metro Line L9 Sud. It also excludes the aerobus. Obviously, you should read up on what the travel cards cover prior to making your trip, but it is not as complicated as travel websites make it sound. Most of the time, it is easier to memorize what the cards “don’t” cover, rather than trying to figure out all the routes and modes they do cover.
You may buy metro travel cards on buses, online, at tourist offices and you may buy them with the vending machines located in a Metro station. The vending machines do not always accept cash, so you may have to use your bank or credit card to buy your Metro ticket. Some stations are unmanned, and some vending machines only take change.