I have been CrossFitting off and on for over a year, so here goes:
CrossFit, is, at it’s core, a combination of calisthetics, gymnastics and olympic weightlifting. There is very little “new” in the basic movements of CrossFit. What is new and different is how they are put together.
The gyms that teach CrossFit are called “boxes” and they usually offer an intro class/program called either an “on-ramp” or “fundamentals”. You need to take this prior to signing up for regular classes, and really you want to take it. The movements are not dangerous if done properly (with a few exceptions, I’ll get into in a sec) and the on-ramp/fundamentals is your opportunity to make sure you have form down properly. If the box or gym you go to doesn"t stress form over everything else, run away and find another one. Seriously.
Now, the actual workouts (WODs - workout of the day) are usually fifteen to twenty minutes in length but it’s the longest 15-20 minutes of your life. It can be tough to remember proper form as you get fatigued and that is the danger. Slow down and get your form right, speed will come later. The rest of the hour is warm-up and learning the proper movements.
Your coach should offer you scalable workouts until you are ready.
It’s a fantastic way to get in shape and gain muscle. It worked very well for me and continues to be my “go to” workout.
The movements most responsible for injuries (IME) are the kipping pull-ups and the GHD sit-ups. The latter for rhabdomyolysis. Any coach worth their salt should be aware of this potentially life-threatening situation and yes, it comes from pushing yourself too hard. This is especially tough in CrossFit because the workouts are so short, and you are encouraged to push hard, so you need to know your limits.
So, form above everything, know your limits and have fun. I’m not an expert, but am happy to try and answer anything else.