The rate that your gears are spinning in relation to each other and the clutch gear (who's name i can't remember, I think it's a collar) that engages the engine/layshaft to the wheels.what does "not synchronized" mean?
Meaning that the first gear's wheel isn't spinning at the same rate as the other gears so when you shift to first and aren't going slower the collar and the first gear aren't going near the same speed which is where you get the grinding sound as the collars teeth tries to fit into the gear.