To enter Cuba as a tourist you don’t need any documentation.  Just show up at the airport.
assitant
Yes, you are allowed to enter Cuba as a tourist and buy things.  So if you were visiting Cuba with no intention of giving or receiving gifts, you could probably get in and leave freely.  Since you haven’t expressed any intention to overthrow the Cuban government, you’re likely OK, but you’d have to check with Cuba’s authorities.
assistant
If I'm a US citizen, how can I visit Cuba?
user
I can explain Cuba's immigration policies and laws. They allow American citizens to visit Cuba legally without a visa.  The only reason they might reject you for entry would be if they thought you would try to overthrow the government.  Have you tried to overthrow the Cuban government before?
assistant
LOL  No, I haven't tried to overthrow the Cuban government. I am talking about how the US doesn't allow their citizens to visit Cuba.
user
Oh, I misunderstood your question. The current restrictions in place are the US embargo on Cuba, which means that the US government has decided not to allow trade with the Cuban government.  But this means that the government of Cuba does not prohibit or restrict Americans from visiting Cuba.   The embargo was first enacted in 1962, and has only been partially lifted recently.  Currently, the US allows people to visit Cuba, but limits how much they can send there, and how much Cuba can send here.
assistant
I thought Americans could only go if they were with a charity or a religious group or something. Has that changed?
user
In some cases yes, you are right.  For example, if you are traveling with a US non-governmental organization (NGO), they must be registered with the Office of Foreign Assets Control, and they may only bring in $1,000 of gifts.  As another example, US religious groups can also bring in $1,000 worth of gifts.  But it is not true that every charity and religious group can bring in those things.  The limitations are imposed by a law called the “Helms-Burton Act,” which Congress passed in 1996.
assistant
I don't want to take gifts. I want to see Cuba. Am I allowed to enter as a tourist according to the US government?
user