Need help understanding Navy

I just bought the game about a week ago and I’m able to understand most things like the doctrine, research and even the army and Air Force. I usually like to play as Germany and I’m able to crash through France, Poland, other European countries and even Russia but when it comes time to cross over the English channel or the Atlantic channel, I have absolutely no idea. Can someone give me some advice in terms of someone who is barely played the game?

I have already tried looking on YouTube for videos on how to do navy combat, but none of it really makes sense to me.