Phonologie

Glen told me once I neew a phonologie lesson and I tried to accomodate
me with the idea.
And I got a big problem regarding the .. labiovelars.
I fail to see how a human mouth will change the "qW" to "p" and the "gW"
to "b".
I try to round the lips as a horse, but there is nothing which will
resamble an "p" or an "b".
It looks still like an axioma to me, but I was not able to find the
demonstration of it.
Any talented person who can explain this changes practicaly?

Alex