Sit down on a bench and place your elbows on your thighs making sure your wrists have enough clearance from your knees. You will grip the barbell with your palms up at shoulder-width apart. This is your starting position.
Curl the bar up as far as the natural range of motion in your wrists allows. Then, lower/curl it back down as much as you can. Finally, repeat this entire movement for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Don't allow the barbell to jerk your wrists down too fast as this may result in injury; always be in control of the weight
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or increase the weight.
This is a classic forearm exercise. The movement is easy to execute and it will build your forearm muscles fairly quick. After doing this exercise for a while (4 to 6 weeks) you should move on to more advanced forearm exercise that involve the use of dumbbells. Forearm muscles are small and to keep them challenged you need to mix up the variety of exercises you hit them with.
Also, keep in mind that if you experience some soreness in your wrists for the first while, this is normal. If you have never done forearm exercises before it will take some time for your wrist joints and ligaments to get used to the stress placed on them.