please someone say smthn

It's as simple as just getting good and trying different combinations of shapes- you will get there. But you could try alternating between having an inverse pyramid placed on the inside side of a pyramid and then ontop of the next, so one so forth. This will make the shape you build slope inwards and upwards, which you can't do with the default 'hold LMB and drag'

I would try making a cross section of the stern along the red (x axis) symmetry grid (without the rudder), and try to make that cross section connect with the hull shape along the z axis (blue symmetry). You could also search the workshop and look for methods most people use.

I always say this. Build it like a real ship. Lay your keel. Every 10 blocks, build a "frame" or "rib" in the shape of the hull in that location. Once you have a frame, just find a clean way of filling them in one frame at a time. If you get stuck, start in a different area and work backwards. Then zoom out and see if it works.

Depends on what kind of stern you're doing, but if you want that long rudder post Titanic booty, try building a rear facing "bow" to get the taper right, lay your poop deck on top of it overhanging in the shape you want and build down into the taper. Flat transoms are easy but boring to look at- but can be spiced up with easily placed paint blocks for ship names and ports of registry. A cruiser stern is fairly easy to pull off if that's the era you're going for.

Lastly, you can find deck plans for thousands of ships. Save an image that you like and you can stick it in a photo measuring tool like https://eleif.net/photomeasure that will let you measure distances off of two known points to get an idea of scale when laying things out.