Lie down on the floor and rest your heels (whole foot if you can) up against the frame of the weight stack. With your arms down, grab the bar with your palms facing up and at shoulder-width apart. This is your starting position.
Curl/lift the weight as far up as you can (as far as your natural arm movement allows). Then, lower the weight back down to the original starting position and repeat entire movement for the desired or prescribed number of repetitions.
DO
DON'T
Perform this exercise in a smooth and fluid motion
Don't push off with your legs too much because this is cheating and does nothing for your biceps
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or increase the weight.