Yeah pretty much what the guy said above.
The skis will be ground, any gouges filled, ground again around 2-3 times on decreasingly less course belts. Then the bases will be stone ground next. The stone is dressed with a diamond to give the structure pattern. Generally for warmer wetter snow you will have quite a deep liner structure, to aid in water being passed down the base. In colder dryer conditions, a less deep cross hatch pattern might work better, as there is less suction on the base. Basically you try to get the least suction on the base, so for wet snow, the deeper the structure the better.
Shops will generally have a lot of predefined settings for the stone structure, as well as some custom ones, if the techs like to experiment. Most shops will be happy to dress the stone for you if you request a certain structure.
You will want to detune your edges again after, as they will become sharper, but detuning a sharp edge is better then trying to deburr then detune an old beat up edge.
One thing to note, if you have really beat up bases and edges, shops may not grind your skis, as they could end up damaging the very expensive machine.