Hold the DB in the same hand as the leg that will be stationary.
With the DB against your thigh, have your chest up with a braced core and neutral spine.
This will be your starting stance.
Eyes are focused straight ahead with a neutral neck position.
Bend/hinge slowly at the hips maintaining flex in your knee, lower the weight (and your torso) straight down your legs while raising your opposite heel towards the sky.
You will feel the maximum stretch in your hamstrings.
The bottom position will be roughly knee-level.
Upon reaching the max stretch, begin lifting the weight back up via hamstring and glute utilization until you reach the starting position.
*Tips*
Keep the DB close to your center-of-gravity.
Keep a slight flex in both knees at all times.
Don't let your low back arch excessively.
Ignore the notion to lower the DB as low as possible.