How do database applications work?

Question

Android

Interested in such a question, I just can’t understand: all the mob. applications that work with databases, how are they arranged (telegram, vk, fb, etc.), and how do they connect to their database? With the UI, everything is clear, it goes in the application itself, but not with this moment. They do not work through WebView or iframe when, for example, index.php is on the server and immediately processes everything.
1.How is the connection to the server and database going?
2. Is it possible to do such manipulations with hosting?
3. If possible, give an example

Answer 1

The application accesses the site via the web API (http/https/socket...)
And the backend of the site accesses its database, prepares a response and returns it on this request in a convenient form (text/xml/json/raw)