I guess it is wrong to ask why they built a ramp on their carriers and how it helps...
They don't use catapults so they need the ramp to provide the extra 'ompf' for the planes to get off the deck.
The simple way to explain it is that they basically have retractable chocks/blocks that hold the aircraft wheels in place at the bottom of the ramp. The aircraft goes to takeoff power and when they are ready they chocks/blocks are retracted into the deck and the plane accelerates up the ramp and takes off.
The reason they did this is that it is a lot easier to do than designing, building and operating catapults along with modifying aircraft to use them. There is a reason we are the only ones left in the world that make them (the French CVN
Charles de Gaulle uses American made catapults) and everyone else uses ski ramps. The expense and complexity is just too much for the rest to bother with. The
INS Vikramaditya, India's modified Kiev-class CV that is being modified by the Russians, will use the same system.
The penalty to using this system is that the aircraft can only take off with much lighter loads, the Su-33's and Su-25's (only used as trainers) off the
Admiral Kuznetsov are limited in how much fuel and ordnance they can carry.
