Role of arms is to move up, down and up. The body moves(turns) with them. The body turns so arms can swing up.
LEFT SIDE OF THE BODY
Particularly left arm and hand move the clubhead back and up to the top in the backswing.
Left arm create a swing arc. In order to get a correct position, the body must turn properly.
Once reach to the top, swing left arm down to the ball, taking the same path. The body turn needs to be reactive.
HOW TO START THE BACKSWING
There is always a trigger to start the backswing. That trigger is the right hip. Move it slightly to the right side, this move pulls the left hand and arm and the clubhead back and up.
HOW TO START THE DOWNSWING
As the clubhead reaches to the top, the left leg and left hip start opposite direction. This is how centrifugal force is created and the way to accelerate the clubhead speed.
AT THE TOP
Shoulders are turned 90 degree and remain 90 degree as the downswing begins. Keep fully turned position and swing the left arm and hand toward the ball. If you did correctly, lateral shift (balance moving to left)should take place as left leg move.
As the left hand enters the release area, right foot and right knee kick in and snap the right hand into the shot. Shoulders should be square timing at impact.
SYNC HANDS, ARMS AND SHOULDERS
Your left hands and arms and shoulder should work in sync.
Keep your right arm at the same distance from your torso on your takeaway.
SHAFT POINTS BUCKLE
Shaft still points at belt buckle at clubhead 8 o'clock.
Legs are quiet and feel weight inside right foot.
Throughout the takeaway, clubhead, shaft and hands are in line with belt buckle.