There is a lot of information across the web about boot fitting. As a skier or parent of a skier, you need some basics to have an intelligent discussion with the boot fitter of choice, so these are good enough:
See Ski boot setup for more details or the different sources below.
Otherwise, for coaches and parents wanting to know more, Here's a selection of articles.
Boot fitting articles and forum: Ask the Boot Guys
Good article on boot canting principles: www.epicski.com/a/boot-fitters-alignment-is-key-says-dr-d
Good set of articles on boots: www.howtoski.net/sub_boots_leadpage.html
For do-it-yourselvers, here's a great resource: www.skibootalignment.com/page9.html.
Another great discussion on race boots for young athletes:
and more race boot fitting intros:
Nomal coaching dogma says softer boots are better than harder boots... well, maybe so, but be sure to read these:
Here are some ideas on how boots are customized:
This is a great video again on boot fitting and how to put the boots on most efficiently:
If you have any questions you can ask them on this forum.