This movement is used to build mass in the bicep muscles. This movement will also work the muscles of your forearm, just like any other bicep curl.
Attach a straight bar handle to the low pulley on a cable machine. Stand facing the machine about one step back from the machine. Pick up the straight bar attachment and stand up straight; the bar will now be at your waist with your arms extended. Grasp the bar with a grip just wider than your shoulders and keep your elbows tight to your body. Next, squeeze your biceps and pull your forearms up to your shoulders. Squeeze the biceps as hard as you can at the top of the movement. Next, slowly lower the bar back to the starting position and repeat.
Keep your elbows still and tight to your body throughout the entire movement; they should be used just as a rotation point. Your forearms should be the only body part moving during this position, avoid the tendency to cheat by moving your upper arms or your back.
There are a variety of attachments that you can use to do cable curls and you can also do bicep curls with dumbbells or a barbell.