The Destroy Object behavior will remove the selected object from your scene immediately when the behavior is executed. Once your object is destroyed it no longer exists, and no other object or behavior can reference it.
This is the object you want to destroy. By default the current object is selected, but you can tap the graphic and choose any other object in your scene.
This outputs the Object ID.
If you want to remove an enemy from your scene after the player has shot it, use the destroy object behavior. Additionally, the destroy object behavior can be used to improve performance by removing objects that are no longer needed.