Can someone explain for me how the exchanges is making money when I use their leverage service ?
Do they make money also when prices goes up and I earn money ? Or only when prices fall and I loose my money ?
Take into consideration that when the price is going up the future you are buying is priced higher than the spot price but when the contract closes, the spot price will be used...
Not necessarily. The situation when the price of a futures contract is lower than the spot price is also quite possible. This situation is known as
backwardation, i.e. the reverse of what you describe (which is called as
contango).