Loft refers to the angle of the club face which has an effect on trajectory and distance. Generally, experienced golfers who produce high clubhead speeds prefer lower lofts (under 10 degrees) while novice golfers benefit from higher lofts.
Flex refers to how much the shaft of the golf club bends during the swing. There are generally five ratings for flex: extra stiff, stiff, regular, senior, and ladies. Your optimal flex will vary based on your technique and driver distance.
As shown here:
Flex
Driver Distance
Extra stiff
Over 275 yards
Stiff
240-275 yards
Regular
200-240 yards
Senior
180-200 yards
Ladies
Under 180 yards
A golf tool, also known as a torque wrench, is used to take apart the clubhead and shaft in order to adjust loft and lie, and weights on the sole of the club. Most torque wrenches are universal and will work for any driver or fairway wood.