You can do this on one leg, which requires balance and ankle stability. Or you can do it using a staggered stance, in which case your rear leg will assist with the balance by touching the floor lightly behind your front foot.

Single-Leg RDL

Staggered Stance RDL

While the hamstrings are the primary muscle involved, the glutes will remain active as an assisting muscle group throughout.

The key to a textbook Romanian deadlift is the hip hinge. Without a good hip hinge, you're unlikely to get as much engagement and may struggle to feel much of a loaded stretch.

How To Do It

1. Start in a staggered stance with most of your weight on your front foot and only the toes of your rear foot touching the ground behind.
2. Either lift your rear foot off the floor and raise the leg while hinging your hips back or, if you opt for the staggered stance, hinge your hips back first while keeping your rear foot in contact with the floor.
3. While hinging your hips back, lower the dumbbell(s) toward your front ankle. While maintaining a neutral spine, travel as far down as you can. Allow a slight bend in the knee until you feel a good loaded stretch without any unwanted spinal flexion.
4. Engage your glutes from the bottom of the movement and press the hips forward. Keep the dumbbells in one smooth plane as you return to the top position.

Related:
The Romanian Deadlift, Improved

Related:
6 Hamstring Exercises for the Home Lifter