huh. The rules on surprise seem to be missing. Great catch ill make sure to add them back in. In the meantime:
You just roll a d6. Monsters and players are surprised 2 in 6 chance(some monsters vary). Light source modifies this. You roll 1 die for each side (or for players you can even do each player) and that is only rolled at the beginning of a combat encounter in which it is pertinent.