Labour brokering is like when your mom or dad asks your babysitter to come over and watch you while they go to work. The babysitter is a worker who your parents pay to take care of you and make sure you're safe while they're gone.
In the same way, labour brokers are people or companies that connect workers to employers who need their help. The workers can be people who are looking for jobs or who already have jobs but want to work somewhere else. The employers can be companies or businesses that need people to work for them.
The labour broker acts like a middleman between the workers and the employers. They find workers who have the skills the employer needs and they introduce them to each other. If the employer hires the worker, the labour broker gets paid for their services.
Some people like labour brokering because it can help people find jobs they wouldn't have found otherwise. Other people don't like it because they think the workers should be hired directly by the employer, without a middleman taking a cut of their earnings.