There are 2 types of currency used in Cuba. The one used by the common people are called pesos. In the city, CUC is more often used, even though  it was originally created to help foreigners change their money. Usually 1 USD = 1 CUC. However, it's better to bring Euros to exchange, because by law, US dollars are charged a 15% tariff. That's why I changed my dollars to Euros before coming to Cuba. But don't make my mistake of changing into too many pesos. I thought I would use a lot more of them, but even in non-tourist areas, CUC is the standard, even at restaurants.
You can't go to a regular bank, and hotel rates suck. So go to a CADECA.

I was walking in old town and saw a girl passing out flyers. However, when I walked over to take one, she pulled away and refused to give me one. It was obvious that it was a flyer for the paladar upstairs, and I was sure it had lower prices. So I had my friend surrepticiously walk over and grab the flyer. As you can see above, these are very cheap prices! However, when the foreigner goes upstairs to the paladar, he receives a nice menu with 4 or 5 times the rate! You see, there are 2 types of menus: one for the Cubans and one for the foreigners. I refuse to eat at the old town paladars for that very reason, and don't let a "friendly stranger" on the street take you to one.

Instead, there are plenty of "corner stores" that sell cheap food, straight to anyone, foreigner or not, same cheap prices. There was a burger joint near Central Park that had these tiny burgers for 50 cents each. I'll take 5 please! Delicious!