Basic Mechanics (9e)
Rolling Dice
Actions in Nine Elements are separated into two categories: those that need to be rolled for, and those that do not. Something as simple as walking down a street requires no roll, but jumping between rocks floating in a river of molten lava would require a roll. It all depends on difficulty.
Skill checks and attacks require a d20 roll. On a successful attack, you may be required to deal damage, which requires the rolling of damage dice. Each aspect has its own separate size of damage dice. Skill checks and attacks both get a bonus: skill checks from a relevant background, and attacks from the chosen weapon.
Sometimes you will be prompted to roll double damage dice, meaning you roll two dice instead of one. This does not stack: you cannot double twice to roll four dice. You will also gain bonus damage from your chosen weapon, the same amount as the attack bonus. So a weapon that has a +5 bonus will always give +5 to the attack roll and +5 to the damage roll.
Additional damage dice can be granted by special powers or class benefits, but these do not increase double damage dice. If you gain both double damage dice and an extra die on an attack, you roll three dice, not four. Additional damage dice do stack, however. If you have two unrelated sources giving you additional damage dice, you will gain two additional damage dice on your attack.