Introduction to Inscription
Inscription is the process of taking various herbs, milling them down to pigments, creating inks from those pigments, and then creating glyphs, cards, and various other items. It's a great way to add several small, permanent, buffs to your character.

What the glyphs do is enhance one of your character's abilities in some way. For example, Glyph of Eviscerate adds 10% to your Eviscerate crit chance. Other glyphs change cooldown times, cut mana costs, increase ranges, and so on. See below for other items that can be created.

The 3.1 Patch Update
The notable changes to Inscription with the 3.1 patch amount to a bunch of new glyphs amd some changes to existing ones. For details on the changes you can check out the 3.1 patch notes.

The new glyphs introduced to the game with 3.1 are only found through a Book of Glyph Mastery.This book is a World Drop, which means that any mob in Northrend can, in theory, drop it. It can, apparently, also drop from lockboxes. The book can be traded and, as of a few days after the patch, is selling on the Auction House for 2,000 to 5,000 gold, per book. As of this writing it's pretty rare, though not as rare as epic items. Don't count on finding them all anytime soon.

The catch is that the glyph you learn from the book is random. So yes, you can blow 5,000 gold for a glyph which you can't use, no one in your guild wants, and that you can't sell. Or... you might find one which few, or no, people have and you can sell the glyphs for well over 100 gold each.

Makes it fun, no?

How Inscription Works
Basics
Each class has at least a dozen major glyphs, which all scribes can get straight from the trainers, and then several minor glyphs, which need to be researched with Minor Inscription Research. Other major glyphs can be discovered by scribes who have the Northrend Inscription Research skill.

Also see the notes above about the 3.1 patch.

Each of the research skills has a 20 hour cooldown, so 30 days after Inscription went live the most dedicated Scribes only had about 30 total minor glyphs. Obviously, to get this skill one needs to have the Wrath expansion and then needs to get to a trainer in Northrend.

All Inscription recipes are either bought off the trainer or descovered through research, though it's certainly possible that some glyphs or other Inscription recipes will appear as drops off some critter or boss, somewhere.

Installation
To install a glyph you need to buy, beg, borrow, steal, or create an appropriate glyph and then find a Lexicon of Power. Generally these are located next to the Inscription trainers. See below for locations or just ask a guard in a capital city.

Right click the glyph and install it into the appropriate slot. If you get tired of the glyph and want to use a new one, just install it over the top of the old one. Yes, the old one will be destroyed.

If this sounds about the same as adding an enchant to an item, you're right.

Making Things
The basic process to make a glyph, or other item, is this:

Buy a Virtuoso Inking Set from the Inscription supplier.
Buy a stack of the appropriate herb (see below for the herb lists)
mill the herbs into pigments
Process the pigments into inks
grab a stack of the appropriate parchment from the Inscription Supplies Vendor or Trade Goods vendor
Make your items.
What You Can Inscribe
Like any other WoW profession there is more to Inscription than just glyphs. You can hop over to Thottbott for a complete list of glyphs and other inscribed items for your particular class, but here's the short list:

Glyphs, of course.
Scrolls of <stat.> Scribes can create all those Agility/Int/etc. scrolls. Want a bunch of Agility 8 scrolls? Buy them off the AH or ask a scribe.
Shoulder Inscriptions, like this one (self only)
Hunters, change your pet's name with a Certificate of Ownership
Tomes, held of the "off hand," such as Faces of Doom (most are self-only, though this one isn't)
Vellums, which allow enchants to place enchants on scrolls, and then pass them around or sell them like any other scroll. Yes, you can now buy a scroll of Mongoose (if a 'chanter has bothered to make one and post it on the AH)
Cards - Darkmoon cards, and many others, are now being made by Scribes.
Why Inscription is Cool
Why is Inscription cool? Let's see...

Relatively cheap to level - a few herbs are far cheaper than stacks or ore or rare ehchanting mats.
Glyphs are cheap enough to buy that youi can swap them in and out and experiment with them.
Tomes, cards, shoulder inscriptions.
It's about the only crafting profession where you can make real gold, not "just enough" to maybe cover expenses.
Where is Everything Located?
To train up to skill level 300 see the Inscription Trainer in any of the Azerothian capital cities. You don't need to do any special quests at any time, just buy the recipes and promotions from the trainers. Ask one of the city guards for exact directions.

Master level Inscription is obtained in the Outlands, in both Thrallmar and Honor Hold.

Horde, see Neferatti, in Thrallmar, at 52.3, 36.0. Neferatti is located on the 2nd floor of the tower, up the hill in Thrallmar, beside the Master Enchanting Trainer.
Alliance, see Michael Schwan, at 53.9, 65.5. Michael, and his sales assistant Jezebel Bican, are in the tower on the same floor as the master enchanting trainer directly across the platform.
GrandMaster Inscription is obtained in Northrend, in any of the entry port cities linking to the mainland of Azeroth. You need to be level 65 and have a 350 level skill to buy the Grandmaster skill level.

Materials Needed for Inscription
To make any of the ink needed for Inscription yu will need to have some herbs, which is why Herbalism is the perfect companion skill for Inscription. The herbs are milled into pigments, and each milling requires five herbs. Each time you mill a 5 stack you will receive 1 to 4 (usually 2 or 3) common pigments and you might receive a rare pigment. The latter is used for the special inscriptions, such as cards. Generally any stack of 20 herbs will yield 10 pigments and one or two rares.

You them process the pigments into inks (you will pick up this skill from the trainers.) Once you have your inks you will need parchment to create your glyphs and other items. All parchment papers can be bought from the Inscription Supply vendor or the Trade Goods Vendor.

The cool thing about the herbs required is that you can use any of the herbs from a set of herbs, rather than just one herb. To create Midnight Ink, for example, you can use any of these herbs, five at a time: Briarthorn, Bruiseweed, Mageroyal, Stranglekelp, or Swiftthistle. Use whichever is cheapest or easiest to buy/gather, the drop rate of the pigments is exactly the same for each of the herbs in a set.

Mooglow Ink: requires either Peacebloom, Silverleaf, or Earthroot
Midnight Ink: Briarthorn, Bruiseweed, Mageroyal, Stranglekelp, Swiftthistle
Lions Ink: Grave Moss, Kingsblood, Liferoot, Wild Steelbloom.
Jadefire Ink: Fadeleaf, Goldthorn, Khadghar's Whisker, Wintersbite
Celestial Ink: Arthas' Tears, Blindweed, Firebloom, Ghost Mushroom, Gromsblood, Purple Lotus, Sungrass
Shimmering Ink: Dreamfoil, Golden Samsen, Icecap, Mountain Silversage, Plaguebloom
Ethereal Ink: Any Outland herb, such as Felweed, Deaming Glory, Ragveil, etc.
Ink of the Sea: Any Northrend Herb, such as Goldclover, Tiger Lilly, Deadnettle, etc.
Note: You don't need all of the herbs from a group, any of the herbs from a group will do. So use whichever is cheapest. Allso notice that you don't need exotic herbs, such as Fel Lotus or Frost Lotus.

Generally each glyph will require one ink to create, but a few require two. Most glyphs only require one piece of parchment. Items such as Tomes will require more materials, and a very few require mats that aren't inks or parchments, such as the Frozen Orb, required by Faces of Doom.

Leveling Inscription
Leveling Inscription is just about the same as leveling any other crafting skill. Buy a bunch of mats, camp the trainer, buy what skill are available, train the skill while it's orange (if possible,) and so on. Same here, with a couple of differences.

Inscription skills go from orange to yellow very quickly. So the typical routine will be to buy a skill, level your skill by five points, then buy a new skill and level the new one for five points, and so on.
Some of the skills will require the rare inks, so make sure you grind up enough herbs to have those inks.
While it sounds expensive to buy a ton of herbs, keep in mind that you can probably level Inscription from 0 to 400 for less then the cost of a few advanced points of something like Enchanting or Blacksmithing.

Save Your Leftover Herbs and inks, unless you're not planning to sell glyphs.

Penn's Professions Guide
The above guide should be enough to get you up and running with Inscription. If you need or want a lot more detail then you should take a close look at Penn's Professions Guide. That guide will give you in-depth coverage of all of the WoW professions and what it takes to level them as quickly, efficiently, and as cheaply as possible. All of the WoW skills are covered and the guide is updated on a regular basis. For the total scoop on Penn's and to grab your copy, go here.

Massive Gold with Inscription
I've made well over 50,000 gold (see pic) with inscription since it went live, one month before Wrath was released. (As of the 3.1 patch that number is much higher.) So there's gold to be made there, but it does require a bit of work on your part. Make glyphs and post them at the right price. Ooooo... tough stuff. There's a bit more to it than just flooding the AH with your glyphs, though.