Brokers & Exchanges are two different bodies that work in tandem with each other all the time.
An exchange is a platform on which the trading of assets occurs. A broker, on the other hand, acts as a middle man between the customer and the exchange platform.
The broker aims to get his customer the best deal possible in exchange for a commission. And often, will get a better deal than traders going directly to the exchange.
Examples include Riot Blockchain, Cowen Inc and Gain Capital Holdings.