main shaft = vertical shaft with main drive gear near the bottom and rotor head assymbly on the top

feathering shaft = horizontal shaft with blade holders on each end (blades pivot on bearings that ride on the feathering shaft)

tracking = a way of determining if both blades are creating an equal amount of lift. If you have the helicopter rotor blades spinning near or at flying speed and you look at the blades from the side and at the same level (wear eye protection!) you can see if the blades are tracking correctly. if the blade tips are at the same height and look as if they are following the same path then they are tracking correctly. if you see one blade higher than the other then the high blade is making more lift. normally you would either decrease the pitch of the high blade or if desired, increase the pitch of the low blade one turn at a time until they track correctly. If you are having trouble getting the blades to track correctly, that can be an indication of a bent feathering shaft.

balancing is pretty obvious. I found the other day that one of my flybar paddles weighed considerably more than the other. I drilled little holes in it until enough weight was removed to make the two equal. you have to do that with the main blades also but use some tape on the light blade to increase its weight to match the heavy blade. You could also use tape on the light flybar paddle to make them equal weight.