Choosing the multicurrency option
Multicurrency is optional; if all your business is conducted with customers and vendors using US dollars, there's no need to take advantage of this feature.
If you do want to use Multicurrency, you'll need to mark the I Deal in Multiple Currencies option in the System view of the Preferences window. (Setup > Preferences > System)
Once you begin recording multicurrency transactions, you won't be able to unmark the I Deal in Multiple Currencies option.
Setting up multicurrency
You'll also have to perform a number of setup steps. (Setting up Multicurrency) For example, you'll have to set up special accounts to track the transactions you make in each currency. If you plan to make sales in British pounds, for instance, you'll need to create a separate Accounts Receivable account for your sales to customers in the United Kingdom. Every foreign-currency account you create will require a companion account known as an exchange account to track changes in the value of the transactions assigned to the account. (Understanding exchange accounts.)
Only balance sheet accounts -- asset, liability and equity accounts -- can be assigned a foreign currency. All other types of accounts are tracked using US dollars.
Your local currency is set up automatically for you. Because this currency is used to determine the value of all other currencies, it can't be deleted, and its exchange value is fixed at 1.
Specifying currency for foreign customers and vendors
Before you begin entering transactions, you'll also need to specify the proper currency for all your overseas customers and vendors. Only one currency can be used for each customer or vendor (unless you choose to set up multiple cards for them); this ensures that your records remain accurate, and it speeds transaction entry.