First, measure and mark your button placement. With the hole saw attached to your power drill, center it over a button location and drill down into the foam. How deep you drill into the foam depends on how thick your foam is, but for 2″-thick foam like this, I usually drill all the way through.
The diameter of the hole saw should be 1/2″-3/4″ bigger than the diameter of the button.
Now you have deep circular holes to tuck the buttons and fabric into. Stay tuned for another tip next week!