What do you need to do on the server when learning AJaX?

I teach myself how to make web pages and want to use ajAx technology.
Doesn’t his technology require the browser to request information from the server, then the server responds and returns the information, and then the browser processes the information?
I am local (the computer where I study), how should I operate without a server?

If I have a server, what should I write on the server to receive requests from the browser? returned messages? Is it using javascript language? Or do you need to use Node.js and PHP to operate the server?

I hope someone can give me some knowledge. Thank you in advance.