The thumb shifter on all new Campy shifters enables the mutiple shift. It operates basically as a ratchet mechanism. One gear = one click. Five clicks = five gears.
Its perfect for heading up a hill. All you need to do is mash both thumb levers. Drops it to the small ring and drops it enough on the rear cog to smoothly transition into climbing.

In the previous generation, there were certain levels (Veloce and Centaur) that adopted the Escape mechanism, which was basically one thumb push per shift, without the ability to ratchet through the cassette.