Dumbbell on your back, hinge it back.
Keep your back flat and chest proud, never let the spine round under the load.
With the dumbbell held at the base of your neck, hinging forward loads the hamstrings through a long stretch while your back works flat out, literally, to hold a rigid spine against the leverage. The glutes then drive the hips forward to stand you back up. It teaches the hip hinge with modest weight and high accountability, which is why it earns a place before and alongside heavier deadlifting.
The RDL holds the weight in your hands, the good morning holds it high on your back, which multiplies the leverage against your spine and hamstrings at much lighter loads. RDLs are the heavier builder, good mornings the strict hinge teacher. Most people benefit from both.
Until your torso approaches parallel or your hamstrings hit their end range with a flat back, whichever comes first. The moment your spine starts to round, you have gone past your range, so stop shy of it and let flexibility catch up.
Cup one end with both hands and rest it against the base of your neck and upper traps, not on bone. Keep it snug to your body throughout. If it still feels wrong, the dumbbell may simply be too big for the hold, so size down.
