Using a Preacher Curl Bench take an EZ bar which is the bar that had a curve rather than a standard straight barbell or you can use a Dumbbell and use just one single arm
Move Secure your elbows onto the bench and grasp the barbell with both hands. using the bend for leverage curl the bar upward in an arching fashion squeezing the biceps at the top and slowly return back down to the starting position and complete for reps.
Using a Dumbbell
When using a dumbbell simply grasp just one dumbbell with one arms using the opposite arm to secure your position onto the bench. Again simply curl the dumbbell upward until you have a full contraction in the bicep.

This exercise was made popular by the first Mr. Olympia winner, Larry Scott. Larry had amazing biceps, even by today's standards, and this was one his favorite exercises. This exercise is similar to a preacher curl. However, instead of using the pad of the preacher curl that is angled at about 45 degrees, you use the other side, which is completely vertical. You'll either have to flip the pad around on the preacher curl, or stand in the reverse direction to do these... that is unless your gym has a dedicated Scott Curl Bench. Perform this exercise just like a preacher curl by keeping the back of your arms pressed against the pad as you curl the bar up and lower it all the way down until your arms are almost straight, with just a slight bend in the elbows.