Hey Linnea,
Thats a fairly easy thing to do once you have your head around the basic concepts. Its like if you were explaining your idea to a friend, you need to tell the game all the same rules.
When your spaceship hits a bullet you could have a simple event like : Spaceship On Collision with bullet -> Spaceship, destroy.
If you want your Spaceship to have to health - you need a way to track that health. Add an instance variable (to the player object) or a global variable to keep record.
Now that same event above might look something more like :
Spaceship On Collision with bullet -> Spaceship, subtract 1 from health.
If you have created a game over sign and werent going to have health then maybe something like:
Spaceship On Collision with bullet -> Spaceship, destroy.
-> Create Game over Sprite at X,Y.