Either way you don’t have to provide the full currency value to open your position. Instead you put down a margin deposit, which is a fraction of the full value. And you don’t actually buy or sell any currency: you are opening a speculative position on the change in value of the forex pair. Your profit or loss is realised when you close your position by selling or buying.
In this case you are right and the spread for EUR/GBP falls to 0.8312-0.8313. You decide to buy back your €10,000 at the offer price of 0.8313, a cost of £8313. The cost of buying back the euros is £111 less than you originally sold the euros for, so this is your profit on the transaction. Again your profit is determined in the second currency of the forex pair.
One unique aspect of this international market is that there is no central marketplace for foreign exchange. Rather, currency trading is conducted electronically over-the-counter (OTC), which means that all transactions occur via computer networks between traders around the world, rather than on one centralized exchange. The market is open 24 hours a day, five and a half days a week, and currencies are traded worldwide in the major financial centers of London, New York, Tokyo, Zurich, Frankfurt, Hong Kong, Singapore, Paris and Sydney - across almost every time zone. This means that when the trading day in the U.S. ends, the forex market begins anew in Tokyo and Hong Kong. As such, the forex market can be extremely active any time of the day, with price quotes changing constantly.