The current spot exchange rate is $1.55/ and the three month forward rate is $1.50/. You enter into a short position on 1000. At maturity, the spot exchange rate is $1.60/. How much have you made or lost?

I know the answer is lost $100

1000x(1.50-1.60)

BUT can someone please explain this to me. What is happening? What does buying a short mean in this case? How much as we paying for them and how much are we selling them for? Please, I'm just trying to understand this. I thought it was $100 profit. Thanks