I did a quick search around the place and couldn't find much information about Glyphs, which are crafted through the new profession, Inscription, and alter spells and skills in some way. So here is my self-gathered information from beta.
Your character has three major and three minor glyph slots. There is a tab in your Spellbook which switches to your glyphs. To equip a glyph, you must be near a Lexicon of Power. Just ask a guard in any city where you can find one. The one in Ironforge is in Thistlefuzz Arcanery, floating above the table on the first floor.
When you click your glyph to apply it, the Spellbook opens automatically to the glyph tab and the appropriate glyph slots begin pulsing -- ie. if you click a major glyph, the three major glyph slots will pulse.
To apply the glyph, just click on the appropriate glyph slot. You will cast for about three seconds to apply it, then the grid will light up and the new glyph will appear. You can Shift Right Click to remove any glyph. Once removed, you will have to buy a new glyph to replace it because the glyphs themselves are consumed upon application.
My recommendation is to choose wisely what glyphs you wish to use, unless you are an inscriber and can craft your own. I have no idea what any given glyph will sell for when the expansion goes live, but because they are consumable, they shouldn't be too expensive -- at least after the initial boom in the market dies down and prices normalise.
It's also great that you can essentially have six glyphs equipped at any given time (seven, if you are an inscriber). This allows for great flexibility in the dynamics of any class!
I think that glyphs will affect how people spec -- at least, to a degree. I know that the Glyph of Fireball is going to be a priority choice for me, considering the advantage of proccing Hot Streak. Losing Fireball's bonus DoT is no big deal in the face of gaining more chance to proc Hot Streak and throw out a Pyroblast, which with World in Flames has a greater chance of critting in itself and throwing up a bigger DoT than Fireball ever could. That, plus you have more chance of getting an Ignite, which in itself makes this glyph very worthwhile. XD
Two final things of note: you cannot equip the same glyph in two sockets -- you will get an error message telling you that it is already equipped; also, tooltips are updated to reflect the changes to skills and spells, so there is no confusion as to the effect that each glyph has.
I look forward to this addition to the game. Polar Bear Cubs are so cute!
Gaiwyn of Proudmoore