Whoever your history teacher was, he's damn right. Mine said the same thing.

Historiography is looking at the history of history being made. Or to put it in a less stupid way, it's studying the historians who wrote it and taking into account their views, biases and preconceptions. Like, when reading a book you go 'This was written in yada yada, by a known Marxist, who had these as his sources for his information'.

You need to understand that everyone has a bias or point of view. This influences their arguments, their presented facts. They'll push one line of thought, cherry pick facts, etc. Reading one book on something limits your understanding.

For example, let's say you study the French Revolution, there's several schools of thought. Primarily, there's the Marxist view- the people were rising up as one, power to the people side to thinking- and the Revisionist view- the people were a force, not the force. They attribute the Revolution to the bourgeoisie, liberal nobles. That's a really rough outline, but you get the idea.

So when reading up on the French Revolution, you read from both schools of thought- not just a single book, you read a lot. And you yourself refrain (or try anyway) from forming an opinion at first, you just find out what they think. Even if you disagree. If you read just Marxist books, you'll think it was all the people, it proves Marxist theories, etc. If you read just revisionists, you'll think the people had only part of the role.

It's crucial to the study of history because it gives us a clearer picture of what's going on. Or to refer to Napoleon, history is a set of lies agreed upon. A single point of view narrows our understanding of history. We know less, and think simpler. There's never one reason something big happens in history, there's never one opinion on it. And more importantly, what the victor and the loser have to say will differ wildly- but both are valid accounts.

I think historiography stems from a school of thought called 'Post-Positivism', the concept that bias affects all work on social events. In political theory, it's called post positivism anyway. They refer to a concept called 'Double reading'- reading things from two points of view to minimise bias. That's the essence of historiography anyway.

Further reading- http://qcpages.qc.cuny.edu/writing/history/critical/historiography.html

http://en.m.wikipedia.org/wiki/Historiography_of_the_French_Revolution (follow the references, dont trust the articles).