There are two main rolls of the game—the skill check and the saving throw. The basic rule behind these rolls is: roll 2d10, add one of the six abilities, possibly add half or all of your Aptitude Bonus, and compare the total to a target number.
Degrees of success
Sometimes fate blesses or curses a creature, causing the novice to succeed and the veteran to fail.
If the 2d10 roll for a skill check or a saving throw is a 19 or 20, or if the result of a skill check or a saving throw exceeds the Difficulty by 10, you critically succeed. A critical success means the roll succeeds regardless of any modifiers. See how critical successes are handled for attacks.
If the 2d10 roll for a skill check or a saving throw is a 2 or 3, or if the result of a skill check or a saving throw fails the Difficulty by 10, you critically fail. A critical failure means the roll fails regardless of any modifiers.