What does normative and non-normative mean in reference to XML

"Normative" means that it's an official formal part of the specification; non-normative means that it's there to be helpful and aid understanding, but you can't appeal to it in a court of law (so to speak).

I'm afraid that specifications from standard bodies like W3C, just like legal contracts, are written in formal language that the reader is expected to understand. It's worth persevering, because once you've got over the initial hurdle of some unfamiliar language, it's actually much easier to get a definitive answer to many of the kinds of questions that people ask on forums like this by referring to the official standard than by reading the tutorial sites that try to make it more friendly but lose precision in the process.

The reason we divide specs into "normative" and "non-normative" is so that people know which source to trust if they disagree. For instance, a Working Group might write a tutorial or a set of examples or a position paper that contains an error which contradicts the normative specification. The normative specification is the one you should trust.

Sometimes a Working Group will cover the same material in different ways in two normative specs. When they do this, they are saying that these two specifications must agree, and any disagreement between them is an error which must be corrected by the Working Group.