Most have electric motors connected to them that are basically used as generators so the engines turn the electric motors to produce electric current to run all the electronic items on the ship.
Think of it like a petrol or diesel engine driven car... you need to connect the wheels to the engine to make it work... you need a differential to make sure when you turn that the wheels on one side are moving at a different speed to the wheels on the other side so they maintain grip and traction.
You need a drive shaft and gearbox and transmission etc etc.
With an electric drive car you have one electric motor for each wheel and then perhaps a small motor with an electric motor attached to that plus lots of batteries.
The small motor connected to the electric motor uses that electric motor as a dynamo to generate electric current that can be used to power each wheel individually or charge the batteries if they are getting low.
All the electrics on the car like lights and heater and entertainment system all run off the battery now and so do the wheels but add a computer and you can be smart... when going down hills all four wheel mounted motors will create electricity... not a huge amount but instead of draining the batteries they will be adding to the batteries.
With ships it means instead of transmissions and gearboxes and enormous heavy drive shafts you can have small pods mounted under the hull that can turn 360 degrees to manouver the ship even in very tight places. Power generation could become like batteries, so a nuclear power pod could be designed that you plug in to a ship and when it is spent unplug it and remove it and replace it with a new one with no need to open it and replace the active chemicals like they do now.
You could also place the reactors in areas where you would normally put ballast to balance the ship so instead of dead weight it is actually useful.
You could have four or six per ship and space them well apart so battle damage is unlikely to take out all your power...
In fact a big ship like a helicopter carrier might have 8 battery locations... four might be nuclear batteries and the other four might be conventional batteries that the nuclear batteries could charge up. Once they are charged up you could power down your reactors to extend their life and run off the conventional batteries till they get down a bit and then power up one or two reactors to run things and charge the batteries up again.
When you need lots of power bring them all online...