Forex (Forex, sometimes FX, from English. Foreign Exchange — "foreign exchange") market of interbank currency exchange at free prices (quotation is formed without restrictions or fixed values).
Maximum liquidity, no commissions and a market from Monday to Friday will help to maximize Your profit.
Profit in Forex is formed by the differences and changes in exchange rates. For example, You exchange 100 euros for $130 and wait for the rise of the dollar and You can sell your $130 more expensive than, say, already for €120 (against €100 invested initially). These €20 and will be your earnings.