An action is something a character attempts to do, that has a risk of failure and where the consequences are interesting in the story. Shooting at bottles could be summed up as target practice. Each shot is not important enough to warrant a roll - therefor they are not actions. When shooting at an enemy, on the other hand, there’s pressure, time constraints, and it most certainly matters whether the bullets hit or miss. That's an action.
Volt uses two distinguishable 20-sided dice. We will assume that one die is black and that the other one is white. An action is a dice roll that is compared to a value; usually an attribute. If at least one die result is below or equal to that value, then the action is successful.
Example: A character tries to patch up a wounded comrade using the attribute Medicine, value 10. The dice are rolled: 12 and 5. 5 is below 10, and the action succeeds.
Tasks are made easier or harder by modifications: a bonus if the task is easy and a penalty if it is hard.
If it’s relevant to determine how well a character succeeds, look at the highest successful die. The last example is a 5 Success. If no die is successful, the highest die rates the failure instead. A high successful roll is better than a low successful roll, and a high failed roll is less of a failure than a low failed roll.
The result is objective - not relative to an attribute or difficulty. That means “5 Success” is equally good regardless of the attribute. Increasing an attribute unlocks higher results while preventing the worst failures. For example, “15 Fail” represents the same modest level of ineptitude or bad luck for everyone. A slight overcompensation for the wind, missing one subtle tick of a pin in a tumbler lock. It happens to the best. If your attribute value is 12, then 13 is the worst failure you're still capable of.
When it is possible to add 20 to the dice and still succeed, do it.
Example: After applying several bonuses, an attribute is 22 for one roll. The dice show 16 and 1. The action is a Success of 21 (1+20).
You never roll this way using Melee, Ranged, or Stealth. These attributes are modifiers to other rolls.