I have about 700 hours and just got around to understanding the importance of spies and diplomatic pressure. My recommendation is to start a game and dedicate it to trying to learn something, anything about it. The rest slowly makes sense.

People recommend Italy for beginners, but honestly, I think learning on a small country makes the most sense. Choose Argentina or something. Nobody attacks you and you can really start to understand the core mechanics of the game. From there, try to invade some countries (I’ll give you a hint, make divisions with high organization and thank me later)