The US has imposed only primary sanctions on Cuba.  The Cuban Assets Control Regulations (CACR) generally prohibit, among other things:

• any transaction by a person subject to US jurisdiction in which Cuba or a national of Cuba has an interest, including the export of goods and services, including financial services, from the United States, and the import of goods into the United States. 
• US persons are prohibited from approving, financing, facilitating, or guaranteeing any transaction by a foreign person that they would be prohibited from engaging in themselves. 
• The prohibitions in the CACR also apply to foreign entities owned or controlled by a US person.

The CACR also further prohibits persons subject to US jurisdiction from engaging in a direct financial transaction with any person that the Secretary of State has identified as an entity or subentity that is under the control of, or acts for or on behalf of, the Cuban military, intelligence, or security services or personnel and with which direct financial transactions would disproportionately benefit such services or personnel at the expense of the Cuban people or private enterprise in Cuba.  Prohibited persons appear on the State Department’s List of Restricted Entities and Subentities Associated with Cuba (Cuba Restricted List), available here.

In an effort to support the Cuban people and private enterprise in Cuba, the CACR contains several general licenses allowing certain activity in support of these policy objectives.  Given changes to US foreign policy towards Cuba, these general licenses should be checked frequently to confirm any relevant authorization is still in effect.