"It" refers to the stem. It clamps directly to a shim that fits over the steerer tube of the fork. To reposition the height, loosen the binder bolt in the back, slide stem up or down, and re-tighten the bolt. What's cool about this system is you can fudge around with your stem and handlebar without messing with the headset.
These stems are set at an angle to the steerer that's 6-10 degrees off of a right angle. That means you can remove the handlebar, remove the stem, and flip it so it's either 90+ degrees or 90- degrees. Most of the time these bikes are sold with the stem in the "up" position. As I said earlier, the stem should be set no higher than flush with the top of the steerer.
It's a proprietary stem made specifically to work with the slotted shim, so you can't replace it without removing the shim, buying spacers, and messing with the headset. If you need more rise, get a mtb bar with some rise, some upsweep, and with the same clamp diameter. You may want to cut off the ends of the bar to duplicate the width of the bar that's on the bike.
This stem doesn't use spacers, it simply clamps onto a slotted ship that fits over the fork steerer tube. I forgot the name of the company that developed and markets this technology, but it's available for any bike that uses a 1 1/8" staight tube steerer, and it consists of the stem, the shim, and the steerer end cap. Scott used it for a year or two on a couple of their hybrid models.
The Scott Subs are cool bikes, like a Trek FX or a Specialized Sirrus but with a more aggressive geometry.