The Disable Object behavior will turn off collisions and behaviors on that object, and any behavior referencing that object. When an object is disabled, it essentially exists in your scene as a graphic and you can not interact with it in any way.
This behavior will trigger an even right when it's executed and your object becomes disabled.
This is the object you want to disable. 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.
Often times, when you "kill" or destroy an enemy you should disable it first. Disabling an enemy before destroying will remove any chances of that enemy hurting you one last time incase an odd collision happens with the physics engine.