Finances support multiple currencies. By default a journal has one currency. When you create a new transaction you can choose the currency for a posting. For example you withdraw $100 from your bank account and get €95 in cash.
2017-01-15 Withdrawal Assets:Bank -$100 Assets:Cash €95
The transaction implies that the exchange rate USD to EUR is 0.95. Finances doesn’t do any exchange rate calculations for you.