To me its more like you should strike with the forefoot but with the foot almost flat (as opposed to running like on tiptoes) so it feels as if you are instantly rolling onto the mid part of the shoe. Or put slightly differently- the middle of the shoe is what catches the groud first as it moves backwards relative to your overall direction of travel. There was a whole huge thing about barefoot running but doing miles of it on grass really did help me retrain as a former heel striker.

Just behind the ball of your foot so as to load your arch in a downward motion. Your heel will almost definitely touch the ground. This, as opposed to a forefoot strike, where you're landing just behind your toes and loading in a rearward motion (think sprinting). Your heel probably will not touch the ground.

Both of these are hard to do in typical "running shoes" which build a significant amount of rubber into the heel, while also being fairly thin up front.

Heel strike - heel lands first

Midfoot strike - heel and ball land same time

Forefoot strike - ball of foot lands first

I've never understood striking guidance either. It seems that over long enough distances everyone is a heel striker too, it's just more efficient. So I'd assume that any advice you hear is more pace-dependent than it appears.