How do the client and server communicate in the case of a normal page?

Question

client-server

If, for example, there is an Android application that accesses the server, then the client (Android application) communicates with the server via JSON. Moving away from mobile applications, let's move on to the web. Question:
How does the client and server communicate if there is a regular web page? There is a site where the user walks through the pages. Here, in the case of an AJAX request, the response is obtained in the form of JSON, and if not Ajax? How do client and server communicate?