How does the throwout bearing engage the pressure plate? I understand it is held in place by the fork which pivots to put/release pressure on the pressure plate, but does it just press against the fingers of the pressure plate when the clutch is engaged? and if that is true, with a properly adjusted clutch, it should not touch the fingers when disengaged...correct?

The sleeve around the tranny input shaft holds the bearing in place. The fork moves it forward and back. When you push on the clutch pedal the fork slides the bearing forward against the pressure plate fingers and the pressure plate moves rearward opening the gap between it and the flywheel. The clutch plate then slips taking the driving force of the engine away from the tranny input shaft. A properly adjust clutch should have about 1 or 2 inches of free travel on the clutch pedal before the bearing engages the pressure plate. Without this clearance the bearing would be constantly spinning and wear out quickly.

Thanks for the answer! I've put on the clutch assembly and bolted on the transmission. A couple more things and I'll be ready to put the engine/transmission back in the car. Thanks again what you said made it clearer and made sense.