The American currency is the US dollar and there are 100 cents to the dollar. Throughout the USA, you can purchase things using either cash, credit/debit cards, travellers cheques (checks) or pre-paid debit cards. However you will find that it is becoming harder to use travellers cheques these days.
Note that if you hire a car, you must have a credit card as the hire company will use it as a security deposit, generally they will not accept cash or a debit card.
It is best not to expect to change your own currency into dollars when you arrive, you are much better off converting your currency before you leave for Florida into a combination of US dollars and possibly travellers cheques (checks) or a pre-paid debit card.
It is worth comparing rates between the high-street, airport bureau de change and online services
Remember the tourist rate you receive will always be less than the published bank rate, especially when changing US dollars back into your own home currency.