Here are some examples:
* "The captain gave orders to steer the ship aft." This means the captain ordered the ship to be steered towards the rear.
* "The cargo was stored in the aft hold." This means the cargo was stored in the hold located at the rear of the ship.
* "The airplane's engines are mounted aft." This means the engines are located at the rear of the airplane.
So, whenever you see "aft" in a nautical context, it always means the rear or stern.