Currency Trading Works

How currency trading, foreign exchange, such as work exactly?
I understand that you buy foreign currency "lots" and depending of whether to increase or decrease the value at the loss of benefits. Do not understand why the coins are paired as "EUR / GBP. Can anyone help me understand the actual process that takes place when people make money?
In simple words: EURGBP = you or use the euro to buy the pound sterling exchange rate is 1 EUR = £ xxx
Currency Trading Tips : How Does Currency Trading Work?