Code examples with ajax?

Question

JavaScript

I am new to programming. I am currently reading Kantor's book on js, + a tutorial on jquery.
In general terms, it understands ajax technologies, there are small examples. But the essence seems to be leaving me) I don’t understand when and how to apply it. How do I understand that this is where I need to enter the ajax request in the code? And how can I understand which one?)
Kantor has a section about http headers. "XMLHttpRequest can both specify its headers in the request and read those sent in response," but he didn't write why they are needed) That's why I decide to get an htttp header as a friend? I don't know.
And a good part of the ajax stuff makes me feel vague. How to deal with this?

Answer 1

about ajax