From what I can tell, this plugin helps you coordinate a zoom webinar with Discourse–allowing you to schedule the webinar and coordinate participants for the webinar from within Discourse. It does not allow you to have the zoom webinar take place within your Discourse page (for example, it does not enable you to have the video appear within a Discourse topic).
When the Zoom webinar starts, users will see a Join Now button in the event page on Discourse, and when they press that button the event will start inside the browser window, taking up the full window. So, the video will not appear inside the Discourse topic, but it will appear inside the browser. (And when they leave the video, they will get taken back to the Discourse topic they were in.)