The idea behind the event besides the dog getting through the course is to judge how effectively the handler and dog are able to work in unison. There are no real restrictions on what type of dogs can compete but dog agility training is not for everyone.
The agility competition has dogs clearing several major obstacles. They are: Contact, Tunnels, Jumps and Miscellaneous obstacles. Training the dog to clear most obstacles will indeed have its benefits come race day. Handlers are generally given a map of the obstacle course prior to the day of the competition. Training the dog to respond to this map will not work well; the map is basically to teach the handler where to call the dog.
Agility training does take alot of work but it is not a difficult thing to teach a dog. One of the easiest ways to start is to use a dog treat to entice the animal through an obstacle. The agility training should start off fairly easy at first and gradually build up in intensity.
The handler's position at the competition is to call the dog through the obstacles. The dog must be a good listener and be well behaved as there are quite a few distractions throughout the obstacle course. What with screaming fans and other dogs barking, one can't stress enough that the dog must be focused on you.
The handler and dog do not come into contact with one another during any stage of the agility contest and so its extremely important the handler, who may not neccessarily be the owner, knows exactly how to get the dog to perform to simple commands in order to get thru the various obstacles.
Much like a coach feels pride at watching an athlete succeed in a competition after having put in all the neccessary hours of training, so too will the handler feel about a dog that succeeds in an agility contest.