Desperately a guide or something to understand armies and war in ck3

So ive been playing for a little bit now, probably around 40-50 hours, and i have just been using automated armies. Thing is, ive really started noticing how shit the ai is for that, and i have absolutely no idea how to do the army stuff myself. I did do the tutorial and paid attention, but i didnt get it back then either. So is there lioe a good yt video guide or maybe just a text guide somewhere? This is pretty embarrassing cuz normally i am pretty decent at understanding game mechanics 💔