To perform an underhand row you will need a horizontal bar placed at the height of your waist. Lie on your back under the bar and grab it with underhand grip (hands facing away). To begin the exercise, start bending your arms at the elbows and pulling your body down until your chest touches the bar. Now from this position, slowly extend your arms until you are back at the starting position. While pulling up, your elbows should go down, along the rest of your body. Keep your body perfectly straight during the whole exercise. As mentioned before you can use a horizontal bar but you can also use anything that fits this exercise (table, chair). This exercise traings your biceps, back (lats) and your arms (delts).

Also let me know if you like the .gif format of pictures for the exercises. Trying this now, but I'm still not sure...