The profit calculator shows your profit (or loss!) in cash and pips given a trading volume, an open price, and a close price.
You need to choose the market you are trading, such as EUR/USD, and set the volume of your trade, either as a number of lots, such as 0.40, or as a notional amount, such as 40,000.
You also need to set the direction of your trade, and the open and close prices.
The calculator will then work out the profit from that trade, both in cash terms and as a number of pips.