Ha! The famous PC muscle. Maybe you heard of it before. There's a lot of information about it that can be found on the internet and in books but all the different sources of information can be misleading and confusing.
In my training program, men learn how to locate your PC muscle (which actually a group of muscles) and how to train it daily. The purpose of training these muscles is to build strength but also to develop dexterity in this area and being aware of this group of muscles.
When you ejaculate, you can notice that involuntary contractions of the PC muscle happen. You can't stop it when it's too late. If you go past the point of no return, your PC muscle will contract to expel the sperm. So the real purpose of training the PC muscle is not only to make it stronger but to gain control over it. You should be able to contract it when you want but also to consciously relax it when you want.
My advice is to experiment with your PC muscle when you practice or when you are with your partner. Every man is different so it's important to know yourself and to know your arousal more precisely. Notice how it feels when you contract your muscles and how it feels when you relax it. Become familiar with how both actions influence your arousal.
Now that brings me to the most common mistakes than men do when it comes to the PC muscle. Don't worry, this is also a mistake that I made in the beginning and I had to figure out by myself that it wasn't working and what to do instead. You are lucky, you will save lots of time and frustration by knowing this already. So what a lot of guys will do is to bring their arousal up and then reaching the point of no return, when they would usually ejaculate. At this point, they will contract their PC muscle as hard as they can to block the ejaculation with their strength. Unfortunately, that usually doesn't work. Sure you can block the sperm from coming out but the
problem is that you still ejaculate. Instead of going out of your body, the sperm goes into the bladder. That's not dangerous because the sperm will go out with the urine but you will still lose your erection and feel the effects of ejaculation. You didn't achieve your goal to control your ejaculation this way.
Other teachers will sometimes teach that this is the way to achieve multiple orgasms. I don't believe it's true based on my experience and my discussions with other men. When you want to achieve multiple orgasm (or if you simply want to have total control), you never reach the point of no return. You go so close to that point that you can have an orgasm. That orgasm usually feels different than an ejaculatory one but is also very good. You always remain in control of you arousal and never go over the point of ejaculation.
Personally, I sometimes contract my PC muscle not to block my ejaculation but to prevent my arousal from reaching the point of no return. I slowly bring up my arousal close to orgasm until I reach an orgasm but I don't reach ejaculation. At this point, between the orgasm and the ejaculation, it helps me to contract my PC muscle consciously instead of letting the involuntary contractions of ejaculation happen. This takes a lot of practice but this is possible. Other times, I need to relax my PC muscles consciously in order to calm down my arousal that is going up too quickly. Sometimes, it's that relaxation that allows me to experience an orgasm without ejaculating.
I know it may sound contradictory but you have to experiment. Contracting and relaxing the PC muscles is a bit like to gas pedal and the brake pedal of a race car. If you use one or the other too much, you can lose control of your car. But if you find the right balance between the two, you will be able to stay in control and stay on course.
Let me add a little something about having multiple orgasms. Men often ask me if they have to stop stimulation at the moment of orgasm. My answer is yes. I have to stop all stimulation at the moment of orgasm in order to experience that orgasm without ejaculating. But right after the orgasm, you can continue masturbation or intercourse because you don't lose your erection and you don't have a refractory period.
Good luck in your PC muscle training!