I call this the fighter's lunge because it sort of resembles the motion of a fighter throwing a knee strike. With this one, you'll perform all reps on one side before switching to the other side. If you're stepping backwards with your right leg, the dumbbell in your left hand should be outside of your left hip, and the dumbbell in your right hand should be in front of your right thigh.
You can perform the reverse lunge with either a forward leaning or upright torso position by stepping backward with your right leg. As you return to the standing position, allow your right thigh to meet the center handle of the dumbbell. With the dumbbell against the middle of your right thigh, flex your hip and raise your knee just above a 90-degree angle with the floor.
Your thigh should meet the dumbbell gently rather than smashing into it. Lift the dumbbell with your hip, not your arm. Step backward again with your right leg and repeat.