CFD means Contract For Difference.
In case of CFD, you are not buying an asset, but you are buying a contract. If the price of asset moves to the right direction, you can make a profit.
Like other investment instruments, CFD has some advantages and disadvantages. It can be a good way how to invest in some specific situations.
For example, if you would like to invest to oil or gas, you don't need to buy them, what will be difficult.
One of the main disadvantages is the overnight fees.