This is a legal or real person who acts as a mediator (ie, conductor). It helps traders to enter the market and make a deal. In fact, it connects the buyers and sellers. Among other things, the broker (or the whole company) can provide additional services to the client (for example, to advise, train, provide analytics, etc.). Of course, for everything that he does, the broker gets commission. It's incorporated in the difference between the Ask price (see), the Bid price (see) and the real market price. Broker's commission is called “spread” (see).
Trading in financial markets involves substantial risks, including complete possible loss of investment capital. This activity is not suitable for all investors. High leverage increases the risk (Risk Disclosure).