That's definitely an important question! You have to multiply the value of one pip by the number of pips you made.
For instance, lets say you bought or sold GBP/JPY at an exchange rate of 148.59 As explained here the pip value for you would be (0.01 / 148.59) х GBP 10 000 = 0.67 GBP per pip. If we assume you're making 25 pips in this position, your profit would be 0.67 pounds per pip х 25 pips in profit = 16.75 pounds.
Now, should we also answer the question "How do I calculate my loss?" ;-)