From a seated position on a mat, roll the spine down until your back touches (or as close as you can get where you can come back up smoothly) then come up pulling your elbows tight to the body. Breathe out as you come up.
Helpful tips and Tricks
You can work a bit more on the "Roll" of the spine and the setting of the shoulders back and down on the body. I was a bit tight on this film session.