CUP or Moneda Nacional is the currency of Cuba. You (the tourist) will exchange your home country’s currency (U.S. Dollar, Euro, Canadian Dollar, etc) for CUP to be able to purchase food, services, and products in Cuba. You can also buy a debit card at CADECA, the exchange at the airport and around the island. This is essential to buy some things, like in the MLC stores. These are foreign currency stores that have most of the items you may need to purchase to prepare your own food, etc. These places will NOT take cash, and many other places these days are not taking cash. Restaurants and taxis still accept cash. You could even negotiate a better rate with your foreign currency directly with restaurants and other vendors.