I will qualify this explanation by saying that regardless of what you may pick up from me, you need to have a qualified instructor watch you carefully to ensure that you arent making any mistakes. Now... here goes my best explanation.
Getting the hands to the gun
Appendix
Both hands drop to let the weak hand establish a solid grip on the cover garment. Lifting upward as high as possible, the weak side hand drives to the high sternum. The strong hand moves just above the grip, into position to draw the gun.
If for some reason youre using an open front garment, the draw becomes more like the 3 oclock draw, just less movement.
3 or 4 o'clock
This depends on type of garment worn to conceal. Closed garments both hands move to the gun position to lift the garment high above the pistol to clear the path for the draw. Open front garments the strong side hand drives inside the jacket, using the little finger to get inside the clothing. There is no flapping the jacket open...that is wasted time and often will flop back onto the gun, fouling the grip and draw. From here on out its the same.
The weak hand anchors itself flat to the sternum. The strong hand moves downward to the gun.
Establishing the grip
In either appendix or the 3 o'clock / 4 o'clock position, the hand needs to drive downward onto the gun. In appendix its a little trickier to do with a closed front garment like a polo as initially both hands are moving upwards. You dont ever want to scoop the gun out with the fingertips and try and establish your grip on the fly. Take your time initially and learn / ingrain the movements.
The thumb slides around the back of the grip to the inside position, ensuring that the web of the hand is in proper position driven high as possible into the backstrap leaving no gap and that the hand is seated in position. The tips of the fingers roll around the frontstrap keeping light pressure on the frame to establish the grip and ensure no snag of inner garments.
Once the grip is established the gun comes up vertically into the #2 position (or #3 if youre running appendix), the hands meet, using the index finger of the support hand to roll against the trigger guard and middle finger of the strong hand. From there the support side thumb extends and anchors to the gun, and the gun and drives out linearly to the target.