To illustrate a FX trade, consider the following two examples
Let's say that the current bid/ask for EUR/USD is 1.4616/19, meaning you can buy 1 euro for 1.4619 or sell 1 euro for 1.4616.
Suppose you decide that the Euro is undervalued against the US dollar. To execute this strategy, you would buy Euro (simultaneously selling dollars), and then wait for the exchange rate to rise.
So you make the trade: to buy 100,000 Euro you pay 146,190 dollars (100,000 x 1.4619). Remember, at 2% margin (50:1 leverage), your initial margin deposit would be approximately $2,923 for this trade.
As you expected, Euro strengthens to 1.4623/26. Now, to realize your profits, you sell 100,000 Euro at the current rate of 1.4623, and receive $146,230.
You bought 100k Euros at 1.4619, paying $146,190. Then you sold 100k Euro at 1.4623, receiving $146,230. That's a difference of 4 pips, or in dollar terms ($146,190 - 146,230 = $40).
Total profit = US $40.
Now in the example, let's say that we once again buy EUR/USD when trading at 1.4616/19. You buy 100,000 Euro you pay 146,190 dollars (100,000 x 1.4619).
However, Euro weakens to 1.4611/14. Now, to minimize your loses to sell 100,000 Euros at 1.4611 and receive $146,110.
You bought 100k Euros at 1.4619, paying $146,190. You sold 100k Euros at 1.4611, receiving $146,110. That's a difference of 8 pips, or in dollar terms ($146,190 - $146,110 = $80).
Total loss = US $80.