How to travel to Cuba as a US citizen

Here's the brief from Ciara's original post:

• 1st of all: US citizens can still travel to Cuba independently or with a tour group!
• I traveled to Cuba independently in December 2017, flew in directly with Southwest Airlines
• Technically "tourism" is not allowed, but you can travel under one of 12 categories
• The "People to People" category under the Obama administration is no longer available as of November 2017, but independent travel & group travel is now available under a new category called "Support for the Cuban People" with the condition where you must spend the majority of your time doing activities that support the livelihood of the Cuban people. E.g.:
• Staying at a Casa Particular(Cuban home/airbnb)
• Eating at Paladares(privately owned restaurants)
• Attending cooking classes, salsa classes, etc. hosted by locals
• You are required to put together an itinerary/schedule for each day before entering the country and keep this schedule on record for up to 5 years if the US decides to verify that your visit met the requirements
• I flew directly from the US with Southwest Airlines. Other US airlines that fly direct include JetBlue, American, United, Delta, and Southwest
• All visitors must have a valid passport, return ticket, Visa, and proof of travel health insurance to enter the country. Note: Some airlines include insurance & visa costs in the ticket price. My airline ticket included travel health insurance. The health insurance must cover medical evacuation by air, medical emergencies, and repatriation
• If your airline ticket doesn't include a Visa, then you can purchase it at the airport at the ticket counter. Tip: The lines can be long, so be sure to arrive at the airport early.