The currency in Brazil is the Real (plural is Reais).  It is pronounced like hay-ow (plural is hay-ice).

The Real is widely stocked in the UK with as much as 8.5% difference between the best (4.33) and worst (3.98) rates on offer according to Compare Holiday Money (April 2015) (5.72 in September 2015, source: holidaycurrencyexchange.com) . The best rates can usually be found online, followed by the supermarkets and travel agents. Avoid the banks and airports at all costs as these offer the poorest rates. 

In the USA you can use a bank or a travel agency to exchange your money.  Many travel agencies offer exchange services, give better rates than banks and don't charge commissions.  In Salvador it is possible to get the official excahge rate of R$2.2 per USD with no commission in a travel agency, by exchanging cash. 

The best place to change money in Rio International airport is with Bank Itau, one of the major Brazilian banks.  From the arrival level, take the escalator to the second floor and turn left.  The exchange booth is halfway down the hall.  The exchange rate (as of September 2014) was R$2.11 for USD, reflecing about 4% comission.  In the Banco Do Brasil down the hall there was a R$60 flat fee per transaction, in addition to taxes.  Safra Bank, at the arrival hall, offered  an exchage rate of R$1.98 in addition to R$37 flat fee per transaction.  

Banking hours are from 10:00 am to 4:00 pm, Monday through Friday.  Some HSBC branches open from 9:00 am to 6:00 pm.

ATM Machines of banks are generally open from 6:00 am to 10:00 pm (although it is common for the locks on the doors to be not operational).  Note that not all ATM machines accept international credit cards.  The machines that do accept international credit cards will have the symbol(s) of the types of international cards it accepts. Banks that typically have ATM machines that accept international credit cards are HSBC, Citibank and Banco do Brasil.

Generally, ATM machines that accept international credit cards are readily found in large cities.  However, if travelling outside the city or to remote areas, it will be much more difficult to find an ATM machine.  So plan ahead.

Generally, it is advisable to arrive in Brazil with at least a small amount of local currency (Reais). If you are based in the UK the Post Office can get Reais for you. You cannot get Reais at any of the airport money exchanges in the UK. If this is not possible, most Brazilian airports have an exchange desk or ATM machines.

Foreign currencies can be exchanged in shops with signs showing "Cambio". The exchange rates given for exchanging cash are generally better than those from withdrawing cash from a credit card from an ATM machine (especially with all of the little fees most card companies charge these days).

Be advised that you may encounter difficulties trying to get cash on a weekend. Several foreigners (from Canada and the USA) have encountered problems getting cash from ATM's after "normal" banking hours on a Friday. This is even from Citibank as well as the local Brazilian banks. Shops with signs showing "Cambio" may also not be in the exchange business on a Sunday.

Q: Can foreigners open a bank account in Brazil?

A: No, not unless you are a Brazilian resident with permanencia and the required documents.