Your audience can access your event by using HeySummit's subdomain, or you can add a custom domain. Head to Event Setup> Settings> Event Domain.
This feature is included under all plans.
You can also change the subdomain of your event to something like "https://bookfairsummit.heysummit.com" using the example from the screenshot below.
If you'd like to add a custom domain, here's a step-by-step guide to walk you through.