An investor wishing to take a position (either long or short) in a futures contract comes in contact with a registered broker authorized to transact on the floor of an exchange.
The investor opens an account with the broker member. Each recognized exchange usually has membership facilities for brokers and this is limited to a few specified limited seats.
The broker collects initial margin money from investors (clients), transacts on behalf of clients, records all transaction details, and reports to the clearinghouse attached with the exchange on regular basis.
Usually, two kinds of brokers are found-commission brokers and local traders.
The former trade on behalf of their client investor and charge a fee in the form of commission on transacted value.
The latter (local traders) trade on them on their own behalf.