Flyball is a physically demanding sport requiring dogs to run at extremely fast speeds, jump, grab a ball, and turn a dime. Dogs need to be physically mature before their joints and muscles are sufficiently developed to handle the stress of this activity. In addition, a flyball competition is noisy, with lots of other dogs, people, excitement, and distractions, so a mature dog that is used to being in a distracting environment and able to focus on the job at hand is necessary. Dogs must be well socialized with other dogs, since this is a team sport, and not aggressive with other dogs, or handlers.
In flyball, teams of dogs are restrained, one at a time, and then released. Each dog runs full speed through two upright poles that represent the gate, down a course with 4 hurdles. The dogs grab a ball from a box, which spring releases the balls at the top of a ramp. Dogs turn using the ramp and run full speed back over the 4 hurdles and through the gate before their next teammate is released. This is a fairly complex set of behaviors to teach a dog, but ball-crazy, motivated dogs usually enjoy learning this activity, and it is good fun and an excellent way to spend quality time with your dog.
If you are training for competitive flyball you will want to simulate a competitive course with appropriately sized hurdles and a spring-loaded ball box, the same as what is used in competition. Flyball uses a tennis ball for your dog to retrieve, and flyball jumps are between 8 and 16 inches high, 24 inches wide between the uprights, and have a spread or base of 16 inches. The height of the jump is set 4 inches below the height a the withers of the smallest dog on the team. Jumps are placed 6 feet from the start line, with 10 feet between jumps.
If you are just teaching your dog for fun, you can set up appropriately sized hurdles that are safe for your dog to jump, and place the ball on the ground, or have an assistant produce the ball.
Before starting training you should ensure your dog is in good physical shape, with no impediments, orthopedic or joint problems, that could be aggravated by strenuous activity. Dogs should also have good off-leash recall, and experience with obedience commands.