If you’re just starting out, it can be difficult to tell if you’re really engaging the PC muscles. After a couple of weeks, the sensation becomes a lot more definite — it feels like you’re opening and closing a valve.
As for how to get started, try taking a piss, then shut off the flow before you finished. Those muscles that you just squeezed? Those are you PCs. A more helpful demonstration might be to work up an erection, then squeeze the muscles at the base of you cock so that your dick bounces up and down. That is essentially a kegel. Now, slow down so that you are holding those contractions for about five seconds, then releasing. That’s the kind of kegel prescribed in the Newbie Routine. (Note: you don’t need to have an erection to do this exercise, it just makes it easier to visualize when you’re new to PE.)
And yes, you do end up clenching your asshole, too. (At least, I do.)