We don't need to get into this, its a mechanic no hoi4 player knows how to actually use so let's move on the next section.

-Click the moodle that pops up at the top of the screen to select all unassigned divisions and assign them to a General using the plus button at the bottom of the screen, assign them to a Field Marshall as well.
-There will be a quadrillion buttons on battle orders but pretend those don't exist for now and just press assign frontline and create an offensive line.
-When you are at war with the country you assigned the frontline to you can press the green button and it will activate your battle plan for your offensive line and troops will attack on their own.
-You can micro units by clicking them individually and attacking specific targets.

Anyways, lets move on to the airforce section since thats just as important as the army unlike the navy.

You might start with no airforce or a tiny one at the very start unless you start as a major. If you are a minor then assign some factories to create interceptors and CAS, its worth it even if you dont produce a lot like Germany or any other Major.

-Assign signal companies to your troops.
They don't provide that much combat bonuses other than giving them more initiative making them make smarter decisions on their own in battle plans. But the reason you'd want them is they increase the amount of CAS and interceptors that can be involved in a single battle. This also boosts shore bombardment if you have a navy at the shore but who uses a navy? No hoi4 player uses them nor knows how to so lets pretend I never mentioned a navy.

-Make strategic and tactical bombers.
Tactical bombers are more difficult to hit by support or battalion anti air in enemy divisions, have more health and do more damage and they can also damage buildings.
Strategic bombers are great if you have air superiority and are well protected from enemy interceptors. You can wipe out a major's factories with only a couple hundred of them so make them!

-Naval bombers
We hoi4 players dont know how to use or even what a navy even is, so make naval bombers to comprensate! It's basically CAS but for the ocean and are better at hurting ships.

Why are you reading this guide? Learn to play hoi4 on your own by experiencing it. Imagine reading guides to play a game. I have 900 hours in hoi4 and still don't know how to use a navy.