In short most nationalities do not need a visa but you need to get a tourist card in advance. They cost about $30.
Visitors should possess an effective passport or a trip document stating their name and the corresponding visa or Tourist Card, excepting those countries that Cuba maintains Free Visa agreements with. Tourist Cards can be requested at the Cuban consular representations.
The airline or tourist agent may give/sell you a visa card.
Cuba visa regulations
Cuban embassies, and embassies in Cuba
