Question about PC muscle

So I just saw a comment on here about the website I’ve been trying to get a prostate orgasm for 13 years with no success (enjoyed the process though) and was just looking around these forums for tips when I ran into the link. Really cool web app, was very impressed with the polish and design. I decided to try the first lesson and immediately got stuck not even 5 minutes in. The instructions are to flex your PC muscle and I realized that this is likely why I am having such a hard time advancing.

I’ve never been able to know how to control this muscle voluntarily. When I’m peeing, if I try to stop the flow of pee mid stream it hurts really bad. Is this normal? Is it supposed to hurt like mad if you stop pee mid stream? I definitely don’t know how to flex the PC muscle or even know where to start with it, and maybe that’s why. Maybe TMI but I am also really bad at holding pee in when I need to hold it. Often it trickles out a bit while I’m trying to track down a bathroom… so maybe I just have a tremendously underdeveloped PC muscle? (In case it’s relevant, I’m a very fit and healthy outdoor athlete, so I’m used to understanding how to control individual muscle groups)

In the “do nothing” technique is it still required that you understand how to respond to sensations with PC muscle flexing? Am I screwed if I can’t find this muscle?