Aircraft carrier
Another deck structure that can be seen is a ski-jump ramp at the forward end of the flight deck. This was first developed to help launch STOVL aircraft take off at far higher weights than is possible with a vertical or rolling takeoff on flat decks. Originally developed by the Royal Navy, it since has been adopted by many navies for smaller carriers. A ski-jump ramp works by converting some of the forward rolling movement of the aircraft into vertical velocity and is sometimes combined with the aiming of jet thrust partly downwards. This allows heavily loaded and fueled aircraft a few more precious seconds to attain sufficient air velocity and lift to sustain normal flight. Without a ski-jump launching fully loaded and fueled aircraft such as the Harrier would not be possible on a smaller flat deck ship before either stalling out or crashing directly into the sea.

Q: What did ski-jump ramps allow STOVL aircraft to do that they couldn't do with a flat deck??
take off at far higher weights