focuses on the movement of the breasts in belly dancing. Notice how the shoulders of the dancer are moving forward and backward, one after the other, to help with moving the breasts. At the same time, her knees are going down and up harmoniously with the movements of the shoulders.
focuses on the movement
Then, the dancer goes to the left and does the same forward backward movements once, and leans to the right. You can see obviously her right shoulder leaning to the right more. The same movement is done on the other side. To the right the shoulders are moving forward and backward, and she leans to the left. The dancer is putting her weight on the leg of the side she wants to lean into by making her knee go down a bit. The movements are simultaneously changing between right and left.
The shoulders movements can also be done to the front. The dancer puts one leg in front of the other, leans to the front, and does the movements. Another way for these moves is the round movements. The shoulders are making the same forward backward moves while the dancer is making a round move with her upper body: right, back, left, front. The round moves are made to the both sides: clockwise and anti-clockwise.
You can try practicing all the moves learned above until you get right.