Answer 1

It's a markup language that allows you to easily tag information so that you can use it elsewhere.

As an example, many years ago I use to do a lot of work with copyright DMCA stuff, and on the takedown requests that we received, it had XML at the bottom that helps contain the information we needed (IP address, date, name of infringement, name the file, etc...).

So why is that even useful? I used a programming language to create a program that would automatically process all of that nonsense for us and submit the tickets (constructive laziness). Because the emails had XML in it, I was able to use the XML tags to extract the data I needed from the emails so that I could automate the process.