Hold a straight bar with the palms up attached to a low cable. Leaning back slightly to counteract the forward pull of the cable and to improve the direction of force, curl the arms as far as possible, and lower under control.  
 
Purpose
The cable curl generally keeps a more continuous level of tension on the biceps than a dumbbell or barbell curl and is a good general bicep strength or hypertrophy choice.
 
Programming
Generally 6-15 reps are appropriate.