those are not real money, but figures on the book.
just like if you have an apple, and a customer offers $1 to buy it. You have not sell the apple, but you assume you have $1 for you have an apple that worth that much.
If there's another customer who offers $2 for that apple, then you think that now you have $2.
But all of a sudden those 2 people refuse to buy that apple but a third person offer you $0.5 for it, then you may think that you have lose $1.5, but the reality is you have not lose anything for you still have not sell your apple.
ok, now if you sell your apple for $0.5, have you make a profit or loss? I can't tell, for it really depends on how much you spent on your apple at the first place.