Certain ATMs at Banco do Brasil, Bradesco and others will have stickers with names of various ATM networks. I have a U.S.-issued Citibank debit card and use these banks plus ATMs of the Banco 24 network (found in many malls, and even Citibank). I haven't been able to use it at branches of Itaś or Santander banks. I use my debit card only for cash withdrawals. For purchases, I use credit cards (I have 3 U.S.-based credit cards, and two of them do not charge foreign currency transaction charges).

Best to call your home bank ahead of time. Fees can vary. I don't pay a fee with my Citibank card, but that's because I'm a Citigold customer. Your bank's policies can vary.

Credit card use is a different matter than ATM use. Visa, MasterCard and American Express are commonly accepted (AE less than the others). Some places even accept Diners Club, which I haven't seen in the U.S. for a while. Most places don't seem to care if you don't have chips in your cc card, though one restaurant we frequent stopped accepting any cc's without chips after the World Cup due to widespread fraud.