Currency gains (losses) occur in two situations.
You deposit $100 USD to an account when the forex rate is 1.5 CAD:1.0 USD. When you spend the $100 USD, if the current forex rate is 2.0 CAD:1.0 USD, a $50 (CAD) gain is realized.
You overdraft your account by $100 USD when the forex rate is 1.5:1.0 USD. When you repay the USD, if the current forex rate is 2.0 CAD:1.0 USD, a $50 (CAD) loss is realized.
The cost base and any gains (losses) realized on currency are shown after each transaction.
Any adjustments to the standard treatment can be made on the Journal Entry tab.