So does the ACTION header on a damage card mean. I know the header is followed by different stuff so

Expample; roll a attack die on a hit or crit flip this card over

An Action: header on a damage card or an upgrade card means "Everything after this header is an action that you can take either by using your regular Perform Action step action or an appropriate free action."

So for a damage card that lets you try to flip it over with an action, you can get to your Perform Action step and announce that you are taking the action on the damage card, and do what it says to do.

As long as the damage card is face up, you'll be subject to the passive/triggered effect (the text before Action:) but once you've flipped it over it's just like any other face-down damage card. It counts towards destruction, but doesn't do anything special.

It means whenever you could normally take an action - in your perform action step, typically, but occasionally from other sources such as Ahsoka Tano's pilot ability, you can take the action on the card to flip it, or roll to try to.