You have many options for getting around in Cuba. For longer trips, there are airplane and railroad services. Within the cities, there are buses and taxis.
The airplane service is inexpensive and reaches many of Cuba's major cities. You can also cheaply visit the Isle of Youth through a plane ride.
The train service is another option. There are two choices, the regular and the especial. Both make the trip from Havana to Santiago de Cuba. Most tourists take the especial, which makes much fewer stops and is the faster of the two services.
Within the cities, you can take taxis, buses, bicycles, or rent a car.
If you choose to rent your own car, you will be able to reach anywhere you want to go. Some roads are in bad condition, but you can drive on almost all. Costs for car rentals will vary, try the Cuban Government's web site for more information.
Many tourists also decide to rent bikes. This will be quite inexpensive, but your mileage will be limited.
The buses in Cuban cities also serve many people. You can also take buses between cities, but the demand for bus transportation far outstrips the number of people that Cuba's bus fleet can accomodate. As a result, you may not be able to get where you want to go by bus. Most buses are uncomfortable, but as with trains, there are first-class services available at additional cost.
To take a bus around town is very cheap. It shouldn't cost more than 5 or 10 US cents. The buses reach nearly everywhere, and will stop when you want.
Your last option is to take a taxi around town. There are both state-owned taxis and private ones. You can call a taxi if you need to, otherwise just wait around and many will come.
Taxis are more expensive for tourists than other ways of getting around cities, but still less than in other countries. You should expect to pay anywhere from three to six US dollars, but can ask and negotiate before you start your trip.
Non-automobile taxis are also available. Occasionally you will see a carriage drawn by a horse, but much more often there are bicycle drawn cabs around. These are inexpensive and plentiful.