The clicker is not inherently meaningful to the dog. Like Pavlov's bell, the dog must learn that it means, "Treats are coming!" via classical conditioning. To do this, trainers "charge" the clicker by repeatedly clicking and then immediately offering a treat. In this way, the dog learns to pair the clicker with the treat. Once the dog knows that a click means a treat, it is ready to start learning new behaviors.
Trainers vary in their methods of eliciting a behavior. Some advocate using food to lure the dog into position. Others simply wait for the dog to offer the behavior simultaneously. Most clicker trainers do not advocate physically pushing the dog into position, as that is counter to the force-free philosophy of clicker training.
Once the dog offers the behavior, timing is critical. The trainer must click at the exact moment that he sees the behavior he wants. If the dog lies down and then rolls over before the handler clicks, rolling over has been marked as the desired behavior, not lying down.
Dogs can learn complicated behavior patterns using clicker training if you teach the sequence gradually. For example, if you wanted to train your dog to jump through a hoop, you might initially click and treat the dog just for walking up to the hoop. Once the dog is reliably walking up to the hoop, you would click only when it stuck its head through the opening, and then only when it walked through. Finally, you would click only when the dog actually jumped through the hoop. The standard for what will earn a reward keeps getting higher as the dog learns each new step. This is shaping.
Rather than giving a command and then teaching the dog what it means, most clicker trainers prefer to introduce the command only after the dog is reliably offering the behavior. Luring motions (such as holding a treat and moving it in front of the dog's nose, then to the ground to teach a dog "down") can be adapted into hand signals for commands by stylizing the motion and eliminating the food lure. Many trainers feel hand signals are easier for dogs to learn that verbal signals anyway, but having a dog that responds to either is ideal. Once a dog is offering the desired behavior, the handler can begin using the command so that the dog learns to associate the two. Eventually, the handler will only click the behavior if it was requested with a command, not when it's offered spontaneously.
It's important to remember that animals are contextual learners. That means that they may understand a command in one place but not another. A dog may be able to sit flawlessly when the handler is standing, but become very confused when the handler gives the command from a sitting position. When training a new command, handlers need to add new contexts, backing up when necessary, to help the dog generalize.
Next, we'll look at how to use clicker training to get your dog to stop certain behaviors.