What do you mean by brushing the ball in tennis?

Brushing the ball means.... Hitting a topspin....

hitting up at a sharp angle behind the ball to make the ball dip and stay in court even when u hit it with all your power.... Magic... now go look for the balls u hit over the fence and start practicing

Brushing the ball generally means going for low to high, and applying spin onto the ball. This is called topspin. The topspin will help the ball get into the court nice and deep.