Forex is a decentralized market with transactions running 'over the counter' with a huge number of participants. There is no official global exchange rate for the market. The exchange rates that you can see in the news and on the Internet come from various sources, but when you open a trade, the exchange rate will almost always be different. That is because:
1. All dealers set their prices according to the buy and sell orders that they are currently receiving
2. Prices depend on the quotations received from the liquidity providers