Africa is a continent, made up of more than 50 individual countries, most of which are autonomous in their sovereignty. Most, if not all, of these countries have their own Central Banks and thus their own currencies.

You can exchange most currencies at banks.

currencies

Depends what country and what currency you are using. Some currencies that are out dated will be accepted by the banks in order to take them out of cirrculation, while some dead currencies are not even accepted in banks, and are just a mere piece of sentimental paper

Banks and firms bought and sold currencies to complete the export or import transaction or to hedge the exposure to fluctuations in the exchange rates in the currencies of interest.