To make the health, make a variable called: health. (don't blame my imaginary with the variable names

)
Actor -> create actor -> Health = 100 (or whatever number you want)
Actor -> collision any side of enemy -> Health = health - 10
Actor -> collision any side of healthbox -> health = health + 10
Actor -> collision any side of healthbox -> destroy collide actor
Then in the draw actor write:
if (health =< 1)
{
destroy actor("Event actor")
}
Now make a text actor and write in it's draw actor:
yourtextactor.textNumber = health;