-snip-
Yeah, my bad, I should have given a better explanation, but yeah it's mostly for safety purposes because most EU countries will begin fighting within a few years and MURICA's only got to worry about building up as their neighbors aren't Hitler or Japan. You could attempt as the Philippines, as you're a protectorate under the U.S. and you'll have a few safe years to build factories and stuff before Japan tries to eat you.
If you start as U.S.:
Start by building Civilian factories in every state asap. You'll be able to convert them to produce weapons later but for now you need them to construct more factories.
Once you have all the states producing factories (it will take a long while), assign a general to lead the national guard using the card thingy at the bottom of the screen. First drag and select all the units on the continental U.S. and then click on the card thingy at the bottom of the screen. This will assign all the divisions to a single army. Now select that army from that card and you'll see a blank silhouette for the leader on the stats card on the top left. Pick a no name general and he'll pop up as the leader for that army card.
After he's ready, you can assign him to defend by clicking on the "garrison area" button at the battle plans popup over the unit card. Just click all the states on the continental U.S. Congrats, the U.S. is now safe from no threats at all! Now that they're garrisoning and moving across the U.S. and all that you can begin generating army experience by clicking on the army card and you'll find the option for them to perform exercises on the army stats popup on the top left. You'll need that experience to customize your divisions for training later.
That's it for a basic tutorial, the game is extravagantly deep and I found learning by focusing on one area at a time will help you learn faster. Like, I had no idea how factories worked until i just decided to build shittons of them.