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 sneak up on a guard using the attribute Stealth, value 9. The dice are rolled: 12 and 5. 5 is below 9, 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 Success of 5. 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.
When it is possible to add 20 to the dice and still succeed, do it. This rule applies to all rolls, including damage.
Example: After applying several bonuses, an attribute is 22 in one roll. The dice show 16 and 1. The action is a Success of 21 (1+20).