When trading an instrument denominated in a different currency than the account currency an FX conversion will occur automatically.
If the instrument currency appreciates against your account currency you will profit, conversely, if the instrument currency depreciates against your account currency you will incur a loss.
To calculate the Conversion P/L, shown in the position details, you need to do the following:
Conversion P/L = (RateClose - RateOpen) * value of position.
Conversion P/L is calculated only for cash products: stocks, bonds, mutual funds, options.