That's a pretty generic statement, in that I'm "learning XML". Not sure exactly what you mean. There's a lots of different aspect about XML to learn.
The basics are that XML is an open document standard defined by the W3C. It's made up of a set of rules that are in line with DOM Model and it's primary goal is to contain data in a simple, lightweight and accessible way.
W3C Schools XML Learning.
http://www.w3schools.com/xml/default.asp