Welcome!
Put simply, if you imagine you have a cup of coffee in your back hand, you want to keep it up and forward so you don't spill it.
Then if you want to go up the wave, you put the cup on the lip, to turn left, you pass the coffee to the left etc.
There's a good introductory video where Clay explains the principles here:
https://train.ombe.co/programs/coffee-cup-intro-coffee-cup-stance-cardboard-surfer
Replied on New to OMBE here, hoping someone can ...
15 Sep 22:36
The coffee cup is always in the back hand, it encourages you to keep the shoulders and chest pointing forward so you can look to both sides and especially back at the foam.