Take a cable in your hands (palms parallel, point to each other), the body is straight. Bend the arms and bring the weight up with a fast movement. Without any pause bring it back down with a slow, controlled movement, but don't stretch completely your arms.

Don't swing your body during the exercise, the biceps should do all the work here. The elbows are at your side and don't move.

The diagram shows the most used muscles on this exercise