Ghana's currency was redominated a few years ago; the paper bills are known as cedis (with the exception of the 1 Cedi coin) and the coins are known as pesewas. Because the redomination exercise was fairly recent in the minds of many Ghanaians, you'll often hear amounts and prices expressed in both new and old terms. For example, when buying a pineapple, the hawker may tell you it's 80 pesewas (new currency) or 8,000 (old currency). When in doubt as to the amount, use the standard Ghanaian phrasing, "say again?" and you'll get clarification.
Most bank machines (ATMs) in urban areas accept debit cards. You may want to check with your bank at home to see if it has an affiliated bank in Ghana. This can save you high service charges as some large banks have agreements with other international banks to eliminate international service fees on ATM transactions. Most ATMs have a daily maximum withdrawal amount, and it may be considerably less than you'd like, so it's best to check with the bank in question. Cash withdrawals using a credit card can be done at designated bank branches, generally the main offices, most of which are located on the High Street in Accra. ATMs seem to work better with cards without a security chip.
Forex bureus, most banks and some larger hotels will exchange foreign currency and take traveler's cheques (See Money Matters). There is a limit on the amount of Cedis one can take out of Ghana.