It’s very similar to playing a brass instrument, basically like a bugle. The easiest way to explain it is that you kind of make “raspberries” with just your lips.

It has been a while since I did it regularly, but from what I remember you blow raspberries, without sticking out your tongue. There was a bit of getting your lips in the proper form.

I used to practice after school while everyone was at work, sometimes I would sit on the living room couch watching after school cartoons and practice the conch during commercials.