Dynamic stabilizer (not highlighted): Triceps Brachii (long head only)
Lower the Smith machine bar to the height of your lower thighs.
Grasp the bar with a shoulder-width supinated (underhand) grip.
Flex your hips and knees and lean forward at a 45-degree angle.
Rotate the bar to unlatch it from the rail.
Keeping your back and neck neutral, exhale as you pull the bar up to your waist.
Hold for a count of two and squeeze your back muscles.
Inhale as you slowly lower the bar to the starting position.
Repeat for more repetitions.
When you have finished, rotate the bar to latch it back onto the rail.
Comments and tips
Do not allow your torso to sway up and down. Keep your body still.
Pull with your elbows, not with your biceps.
Do not lower the bar to the stoppers. Keep it above the stoppers.
The stoppers of some Smith machines might prevent a full range of motion. If so, you can stand on a plate or box.
I would always recommend using a barbell for the underhand Yates row and not a Smith machine. However, some people find that using the Smith machine helps to prevent cheating by way of the body swaying up and down.
Use the Smith machine underhand Yates row to strengthen and build your upper back and arms, and to develop upper-body strength. Of course, you can also use a pronated or overhand grip.