Websites can use APIs in two main ways: backend-tied and frontend-tied approaches. The backend-tied approach is where an application makes requests to the API on the server's side, while the frontend-tied approach uses client-side rendering with JavaScript that fills data from an internal API. To find out if a website uses an API, one can use browser tools such as Developer Tools and Network tab to see requests made by the site. If the requests are not visible in the page source code, it's likely that the site is using the frontend-tied approach. However, if server-side requests are visible, it may indicate that the site uses a backend-tied approach. Python can be used to test this hypothesis programmatically using libraries like Requests.