I once tried a scuba diving open water course. I was taught the basics of dive safety and a few simple skills so that I'll surely be safe underwater.
I learned the straightforward skills needed to be able to dive accompanied by a buddy who is also Open Water certified. Some basic skills I learned were: standard diving hand signals, regulator recovery mask clearing, removal and replacement, fin pivot and proper weighting.
I experienced the feeling of running out of air so I immediately signaled my dive instructor. Eventually, I learned how to continue breathing normally from a regulator that won't stop flowing.
After that great experience open water course, I promised myself I will get/have a scuba diving certificate soon!