CFDs are a leveraged product
Leverage gives you exposure to the markets by depositing just a percentage of the full value of the trade you wish to place. This means that while you could make a potential profit if the market moves in your favour, you could just as easily make significant losses if the trade moves against you and you don't have adequate risk management in place. This is also known as margin trading.
In order to place a CFD trade, you need to deposit a percentage of the total value of the position, known as position margin. If you buy $1000 worth of CFDs and the margin rate for the applicable tier is 20%, you only need to pay a position margin of $200. However, your exposure is the same as if you had purchased $1000 worth of the shares at face value. This means that any move in the market will have a greater effect on your capital than if you had purchased the same value of shares.