One thing that is not easy, is creating a scenario. The plot, which countries, which units reflect the given year, placing units, filling magazines(adjusted to what restrictions the author wants to impose), aircraft and ship's missions that make sense, victory conditions, not to mention the awesome event editor and if you really want to get into it, specific aircraft squadrons, specific SAG compositions, where does country x's 1500+(or whatever number) mobile units should go, what kind of ew radar is that on ge, and the list goes on. The number of things that a scenario author does can be tremendous.
Gunner's tips will get you started. And once you get into it a little more, you'll start to get a great appreciation for those that write scenarios.