We?ve already explained the basic rule that the foundation of the game-roll a d20, add a modifier, and try to get a result that?s equal to or greater than the target number. Whenever your character tries to accomplish something significant, the GM asks you to roll a d20.
Important! Not every action requires a die roll. Roll dice in combat and other dramatic situations when the success of a action is in doubt.
The d20 is used to determine the results in combat and when making skill checks, ability checks, and saving throws. In other words, the d20 determines whether or not you succeed at an action.
The other dice (d2, d6, d8, d10, and d12 ) are used to determine what happens after you succeed. Usually, the other dice come into play after making a successful attack roll to determine how much damage the attack deals to the target.