A floating trem has springs that attach to the claw. Technically the springs cause the degree of float (in guitars that aren't routed under the bridge, the pull of the springs keep the bridge resting on guitar's body.....). If the bridge is routed under the back (like the JP trem and an IBZ edge for instance) the springs hold the bridge at it's "zero point". What that means more or less is that the bridge plate is level and parallel to the body of the axe when tuned to pitch. It's the place the bridge returns to when utilizing the travel, ie dropping pitch or raising pitch as can be done on the floating trems....
Basically you adjust the springs by either tightening or loosening (in the case that you have too much spring tension) the claw screws. Tightening them will cause the back of the bridge to sink into the cavity, loosening will raise the back of the bridge. It's not a hard process, but takes a couple of minutes to get to the zero position if you're no accustomed to doing this. with a little practice you'll be a master. Why pay someone to do it when you can do it yourself?