Hey @joshisplutar
So the API concept comes at play when you want to model a backend API that will be receiving requests and you want to authorize those requests with Auth0. Auth0 will issue Access Tokens to client applications that request them (e.g. a SPA or a Native App), and those apps will include the access token when sending requests to the API.
You define the APIs (a.k.a. “Resource Servers”) in the APIs section of the dashboard, and when creating one you give them a unique identifier. That identifier is what the audience parameter is about: the way for applications to say “I want an access token for THIS api”.
You can read more about this in API Authorization.