To me, XML is a great way to go forward. XML stands for extension Markup Language. It is a meta language where by it used to describe some kind of information.
It uses mainly for web services. Basically it gives you output that can be interpreted by other people. For instance, RSS and google sitemap. All of them makes use of XML to communicate with other system.
Definitely a good thing to learn. I suggest you check out
www.w3schools.com for basic learning of XML