I want a source to learn xml ?

Question

I want to learn xml so that I can save the settings of the programs, I hope that anyone know a book or a website to share me with its name.
and thank you for your support.
note : sorry about any language errors because i am not an English speaker.

Answer 1

https://developer.mozilla.org/en-US/docs/XML_introduction
http://www.tutorialspoint.com/xml/index.htm

Answer 2

https://www.w3schools.com/xml/default.asp