HTTP functions allow you to expose the functionality of a Wix site as a service in the form of REST APIs. If you’ve added functionality to a site with code and want to use it in an app, you can expose HTTP functions and call the APIs in your app’s code. Learn more about Exposing a Site API with HTTP Functions.
Use the http-function module to call your site's endpoints with authentication context. Authentication context is information about who is calling an API. Calling HTTP functions directly doesn't provide them with authentication context, which restricts the Velo functions you can use in your code without overriding authentication using elevate().
Your site's HTTP function's prefix defines which SDK method to use to call it. For example, call the HTTP function get_myFunction() using get().