Barcelona has an affordable and highly efficient urban transport system. You have 5 major ways to get around the city: by bus, metro, FGC (Ferrocarrils de la Generalitat de Catalunya), taxi, and renting a car.
Buses: The city has more than 100 bus lines, which are numbered 6 to 192. They reach more points compared to the metro lines. For the transient Barcelona traveler, however, bus lines are not as easy to figure out.
Metro: 
The Barcelona metro is clean, safe, cheap and easy to use. For most, it is the preferred method of transport around the city. The Barcelona metro system has 6 lines, plus the funicular railway to Parc Montjüic. They are marked by colors and numbers.
Taxis:
Taxis in the city are readily available and they are not too expensive. A taxi ride the center of Barcelona usually costs no more than €7. If you do not mind spending cash, taxis can be the easiest form of city transport. This is especially if you are there for a very short period of time.
FGC:
The FGC trains take you to suburban areas. They leave from two important hubs: Plaça de Espanya and Plaça de Catalunya. But they may also be convenient for going around the Bacelona center as well. Prices vary depending on the zone. You may use integrated passes by zone valid for the FGC, metro, and bus.
Car rentals: 
If you want to hire a car to get around Barcelona, you will have many choices as car rental firms are all over in the city. Hiring a car can be the best way to avoid tourist traps and explore some of Barcelona’s less visited gems.