The phrase "to gather an audience" means to attract and bring together a group of people to listen, watch, or engage in an event or performance. Full definition
Gather an audience of as many people who might become your potential clients at some point. (lawyerist.com)
At first that sort of offering gathers an audience slowly. (discovermagazine.com)
If there is an opportunity, be interactive with your audience through audience polling, gathering audience questions or ask the audience to share their experience. (lmatechconference.com)