For single currency operations, only a system currency applies. However, if you have a multi-currency operation, you can create different currencies here and specify the ones to use for costs and charges.
You can then determine the exchange rates that apply and update them as they alter.
Select Currencies from the Financial section of Administration. A search is processed and you can change filter settings (as described at Searching and Filters to view different records.
Click Add to create a record.
For a listed entry, click 
then:
•Open to access the record.
•Clone to create a currency with the same general details as the selected one. Enter a new code and change other information as necessary.
•Delete to delete the record, providing it is not in use.