The easiest way would be to use 3 Progress Bars. Set their "Max" properties to 100.
I'd probably set 3 global variables (Shield, Armor, Hull) to 100 on start of layout in your event sheet.
Then set each Progress Bars "Value" property to each respective global variable.
Then place with these Actions on your event shit:
System > Every 3 seconds > Variable: Add to > Shield > 5
Make a clickable object to reduce the health:
Create Object > txtAttack > = "Attack" as Text
Mouse> Click > txtAttack > >>> System > Variables > Subtract 20 From > Shield
System > Variables > Compare Variables > Shield is less than or equal to 0 > .... System > Variables > Subtract 20 from Armor
And so on and so forth...
That's how I would start it. But, like you, I am also a novice... just noticed you haven't received an answer yet.