When you trade CFDs and FX you are trading on margin meaning you only need to have a fraction of the face value of the trade in your trading account. You can think of it as effectively borrowing the face value of the trade and putting down a security deposit every time you trade.
If you hold a position overnight it may be subject to an overnight holding cost, frequently referred to as Swap fees. It is possible to avoid the overnight charge by closing your trade prior to the time the funding charge is calculated. You can find more information here: Swap rates: Fundamentals, calculations, risks, types and examples
Discover more about the ThinkMarkets Swap Free account.