One side is the vice that is the flywheel and cover assembly.
They are both connected to the crank shaft. They turn together, carrying the engine torque, and work together to clamp onto the clutch plate. The other side is the assembly that is the clutch plate and gearbox input shaft. Being keyed together, the clutch plate
and gearbox input shaft will always turn together.
To disconnect the clutch, or let go of the torque, you have an actuation system which starts at the pedal and ends at the clutch cover assembly. The Thrust Bearing in a 3 piece clutch kit is one component of the actuation system.
Clutch plate is a disc that slides over the gearbox input shaft. The spline or teeth at the centre of the clutch plate match the teeth of the gearbox input shaft. When the clutch plate slides over the shaft, the matching spline teeth mean the clutch plate is keyed or locked into the gearbox input shaft, and is positioned flat to the flywheel.
The flywheel is one side of the vice. It is a big metal disc that bolts directly to the crankshaft. A small but very strong shaft. At one end is a locating pin that sits in the centre of the flywheel/crank. A spigot bearing sits in the centre of the flywheel, on the locating pin of the shaft. Because the input shaft is not bolted to the crank, it does not turn with the crank, it just uses it as a locating point. The opposite end of the shaft is connected to the gearbox.