There are so many different kinds of stretces that it's just not worth going into it. However, any book on martial arts especially taekwondo wil demonstrate stretches usually within the second or third chapter. Usually right after they are done detailing the history of TKD. But I wll sy this.
Taekwondo today is predominantly a kicking art, so your going to want to stretch your legs out a lot. This usually involves trying to spread your legs out into the splits position.
Don't worry about the stretches it's the first thing you learn, you never start class without basic stretches.
Push ups, sit ups, crunches, knee lifts, squats with no weights. These help, doing squats will really help develop your leg muscles. A very important exercise is jump rope. This helps build up your stamina and endurance. Getsyour heart rate up to get you in shape for those sparring matches.
Learning how to jump high requires that you jump. As you build muscles in your legs you should be able to jump higher. Sometimes setting small goals fr youself helps. In the old days of TKD they had what was called a horse. Basically it was a wooden wall that practicioners would jump over. It was used to help with the flying kicks. Now adays what some people do is they use those heavy hand held kicking pads. The real thick pads that are nearly a foot in width. You can stack them up on the floor and try to jump over them. That way if you knock them down, you don't get hurt.
Or you could have 2 students hold a belt each at one end. You set the height level and then you try jumping over it. As you get better ask them to higher the belt.
Flips and gymnastics are not part of taekwondo. However, there are some schools that have specialized teams that compete in what is now reffered to as extreme martial arts. Bsically they create their own forms for competition mixing traditional moves with modern flashy tricks and flips. Many of these XMAer's have taken a TKD class or two to learn some of the more fancy kicks of TKD. Then they alter them by adding some spins, and gymnastic. Only a smal ammount of schools participate in this though. And depending on what style of TKD your doing. Usually styleis determined by organization but not necessarily.
Basic techniques to all TKD and frankly all karate schools are, the outside block, the inside block, high block, and low block. However, many of the korean arts have a signature hand tchnique, i's usually the knife hand strike/block.
Good luck with your TKD training have fun.
"Poor is the pupil who
does not surpass his
master" - Leonardo Da