This system uses three six sided dice, one of which is different and known as the "Check Digit." Two dice are added together and compared against a target number, where equal to or lower than that target number is a success. The Check Digit is used to determine the degree of success from 1-6.
Rolling 111 and 666 have special meaning (known as 'divine intervention'). In the case of 111, it means God has intervened (1+1+1=3, the Trinity). In the case of 666, Lucifer has intervened (666 = Number of the Beast). This may be a critical success or critical fumble, depending on what side of the Celestial conflict one is on.