Aeropuerto Internacional Jośe Martí contains four passenger terminals and a cargo terminal, most travellers only need to know about Terminal 3 - the International Terminal. To the best of my knowledge there are no bus services between the terminals.
Domestic Terminal - Internal flights within Cuba. I have travelled from here to Santiago de Cuba and back.
US Terminal - Used by flights from and to the United States; a mix of scheduled and charter flights for Cuban Americans and travellers on people-to-people exchange licenses.
International Terminal - Over 25 international airlines, serving over 60 destinations in more than 30 countries. At this terminal euros are accepted at the bars and cafes.
Caribbean Terminal - Includes Cuban airlines, AeroCaribbean and Aerotaxi.