My instructors explain it like so:
1] Stand with your toes and heels parallel and 2 fist-widths apart, or about 6 inches
2] Straighten your arms out in front of you, stretching from the shoulder, keeping them relaxed and strong
[Both the above STAY constant. Try to not drop your arms or replant your feet.]
3] Push your hips back, upper body forward, trying to parallel your thighs to your mat. When you think you’re as parallel as you can go, try straightening your torso so you’re sitting up. The image they give us here is like you’re sitting in an imaginary chair.
4] When it’s time to move on to the next part, stand straight up and come to the front of your feet. You want to be balancing on the balls of your feet/toes. You can think of it alternately as trying to balance on your tiptoes OR trying to lift your heels off the ground. Once you’ve got the balance, slowly bend your knees to deepen it. Try to keep your arms and back straight.
5] Finally, you want to come back to standing straight and squeeze your thighs together. You want your knees to touch too, and this naturally makes your shins angle in towards each other. Try to keep your thighs pressed together as you sloooooowly bend your knees and lower to the mat. Once you’re down, if you’re up for a challenge you can keep your butt raised off your heels by an inch or so; otherwise, gently sit on them. When you’ve made it through a few cycles of breath here, you’ll want to sloooooowly come back up, keeping your arms straight and your thighs still pressing together firmly.
That’s it - you’re done! 
