Clicker training uses shaping, markers and positive reinforcement to develop skills.
You need: your mouth, little edible treats, and a creative spirit.
What I mean by that is I don't use a physical clicker. I, and many clicker trainers, use a mouth click to "mark" a behavior. The click I use is my tongue sort of hollowed onto the roof of my mouth, mouth a little open, and then I pop it. The ONLY time I EVER use this sound is as a clicker. Hearing it makes my horse instantly stop and expect reinforcement (a treat). It is never, ever, ever confused with my other mouth noises, which include a click (sharp noise out the side of my mouth that means "more effort/go faster") or a kiss (which means "lope"), or the word "whoa" (which means STOP NOW), or saying "good" (which means 'you're on the right track'). If you're really struggling making that noise consistent (and that is Very Important), you might need a physical clicker. Sometimes that's best when you just start out, then transition to a mouth click as you gain skill. I put a little wrist hanger on my physical clicker, so I can drop it if I need my hand.
As far as treats, you want something the horse likes, but that is SMALL, easy to feed and quick to chew. I use a specific brand of alfalfa pellets called Estrella. They are the PERFECT size, and about $15 for a 50lb bag. About the thickness of a pencil, and anywhere from 1-3" long per pellet. You can put them in a pocket (I have cargo pocket breeches, my right pocket always has a couple handfuls of these pellets in them. Other popular options are things like the little Manna Pro Bite-Size Nugget treats, or even like Cracklin Oat Bran cereal (one piece of cereal per treat). Whatever your horse likes. You can also have what I call "jackpot" treats for a really super-duper amazing effort. For this I use sugar cubes or peppermints.
Clickering is all about using shaping to your advantage. The premise is the same whether you want to train a horse, dog, human or chicken. Visit Karen Pryor's website for great tutorials on it.
http://www.clickertraining.com/what_is_ ... ?source=nfHonestly the sky is the limit if you've got a good relationship with your horse, and have the ability to break down the shaping process and good timing to mark things correctly.
You see people using it a lot for tricks, but ANYTHING is a "trick". I've played with this a lot, and my horse and I have a long repetoire. None of this requires him having to wear any tack, btw. So for example, I have clickered my horse to:
Smile
Say Yes/No
Give Hugs
Wave
Spanish Walk
Spanish Trot
Fetch
Bow
Wave a flag
Honk a bike horn
Spanish walk, trot and fetch while I'm astride
Stand quietly like a statue
Lower his Head and open his mouth to be bridled
Accept having his ears handled and clipped without a stitch of tack on him
Pick up and hold his feet himself
Carry himself in an "on the bit" body position
Trot with more energy/bounce off the ground
Leg yield
Hip in
Reining Spin
Piaffe
Passage
Etc.
So the point is you pick a behavior. You figure out how you can break that behavior into small enough chunks. And then you play "hot potato/cold potato" with your horse until they figure out what you want them to do. Then you put a word/phrase onto the behavior, and suddenly you've captured it.
I usually use the Spanish walk as the easiest thing to explain. So you start like this: I want to teach my horse to Spanish Walk. How do I do that?
Someone might say, well I'm just gonna tap his front legs until he lifts them. And that works.
But I'm going to say, well, the mechanics of Spanish Walk involves him lifting his front legs up high. So I'm going to use targeting to do this (assumption here is horse already understands the concept of clickering). So my horse and I started just standing still. I have him, treats, and a dressage whip. If I were in a public place (like a boarding barn aisle) I'd have a halter/lead on him for safety. Then I get him to shift his weight enough to bend his knee, just a little. And I have my dressage whip ready right there. As soon as his knee touches that whip, click/treat. Repeat. Pretty quick he'll figure out that targeting his knee to the whip merits a treat. Then it's just a matter of gradually moving (shaping) that knee higher and higher, as he's trying to touch that whip. Then get both front knees, then add in walking. And voila, Spanish walk.
Same deal with all of these things. It creates a horse who enjoys his job, because he gets positive enjoyment out of it (eating), instead of what can be more negative things. It gives you an opportunity to be creative and a better trainer. It strengthens your relationship with your horse. And also it's really damn convenient when you drop a glove or a whip while riding and your horse will pick it up and hand it to you.