Made a RESTful API, what's next?

Question

RESTful API

I don’t quite understand why RESTful API services are needed?
I made a simple restful service on a flask according to a tutorial on YouTube, and I don’t really understand how to use it further?
Why do I need to serve JSON through Flask when I can serve ready-made pages (templates) right away?
If you need to make a client, then what is the client for RESTful API made on? I don’t quite understand how to process this data and make a display out of it (resulting html pages).
Where can I read more about the use of such restful services?

I would be very grateful, because I tried to find information on the use of such services, but everywhere only their creation and advantages are described, but I did not find any suitable information on using them.

Answer 1

Yes, this is done for the client. The client can be a browser, a mobile application, a web application from another developer that receives data from you via api, etc.
In the browser, html is made from the received json using javascript frameworks (vue.js, react.js). In mobile applications - by the internal means of the language, html is also not needed there. The one who takes data from you - also does not need html.
Before writing a RESTful API, you should understand what problem you want to solve.

Answer 2

I'll add on my own - I found an interesting article about the topic:
nordicapis.com/why-you-should-build-apps-with-an-a...
In short: because it allows you to build clients on top of the API on different platforms: iOS, Android, Web, maybe Desktop. Using the API, you can quickly scale your application.
The architecture of the application family built using the API: