The standing hamstring curl machine works the legs, specifically the calf muscles and the hamstrings with some work on your glutes.
First of all, adjust the bottom pad so that your heels sit comfortably against/infront of the pad, and adjust the weight accordingly to you.
To start grab the two bars with your hands to maintain balance. Keeping your hips forward. Then lift back and upwards in a slow and continious motion squeezing at the top.
Seen in this demo is Daniel Ciastoch, a member of the Ascendancy and personal trainer.