We don't really know much at the moment Smokin, we have to just try things and see what happens and to pick apart supplied neocube missions
Activate would probably mean activate an object that has been deactivated. The object already exists in the mission when the mission Begins
There's a tickbox in a plane's/object's properties that will activate or deactivate an object at Mission Begin, before you climb in the cockpit
Spawning is different, the spawning objects do not exist (are not instantiated) at the start of the mission when you climb in, and they do not exist until the Spawn control is activated by a trigger of some sort: your plane gets near enough to a Spawn trigger point, you spawn a flight of planes for example
I used Activate right away but after submitting a mission to neocube's Stepan for help - sorry I forgot to say just now that we have had limited help from the neocube team who've been very busy - he told me that Activate has another purpose
But whatever works of courseSomething tells me that I am going to regret the question.
If (improbably as you've been hammering away, working not complaining) you reply that you knew all that already and that you are not a moron, yep you might come to regret it. We live in hope that you are normal though and of course you must ask any sort of question, the Mission Editor is a complex bit of kit, takes time to get off the ground and is very juicy