The naval mechanics baffle me.
Which parts? I feel like I'm at a point where I can win the naval war as any major nation that really participated in it(UK, USA, Germany, Japan).
Most nations work on the "Fleet in Being" doctrine, which basically means surface ships. Germany in WW2 works on an "Indirect Approach" doctrine, which means submarines.
Fleet in Being
For surface ships, the most important stat is speed, closely followed by range. The faster fleet gets to decide the distance at which battle is joined. If you get to fight at a distance where your enemy is out of range but you are in range, you have basically won the battle, as you can kill their ships and they can't kill yours. That's why if you engage a carrier (which are fast, check their stats), with a battleship (which is slow), they sit at something like 150km while the carrier bombs the battleship to bits and the battleship is useless.
For this reason, carriers are the most powerful surface ships - they're fast, and have a ton of range. Therefore if you have Fleet-in-Being doctrine, you want to get as many carriers into a single fleet as you can.
There are two situations you never want your carriers to get into:
1. Stormy weather. The storm will prevent your carriers launching planes, and the enemy fleet will sneak up on you and get close, and sink you. Avoid fighting in storms.
2. Attack by a large fleet of submarines. Submarines seem to ignore the usual rules for speed and range, and get close to you anyway. Carriers bizarrely have pretty much no sub attack, so you're going to get creamed.
You can't do much about situation 1, but you can do stuff about 2. For each carrier in your fleet, include a destroyer with the ASW attachment. This will give you at least a bit of a chance against subs.
If your opponent IS making vast use of submarines, you can make a fleet of escort carriers with ASW destroyer escorts - that's basically the best anti-sub force you can get. I've never needed to though.
Most nations will have some gun ships (cruisers, battlecruisers, battleships) left over from a time when they weren't rubbish. Blob these up into big fleets of 15 capital ships and 15 screens, and hope the enemy doesn't know how to make a proper carrier fleet.
Indirect Approach
Get 30 submarines. Give them torpedoes. Put them in a fleet under a Grand Admiral. Set them to naval interdiction in the required area. Watch them sink everything.