Uttanasana (Intense Stretch) is a standing forward bend which has some similar effects to Adho Mukha Svanasana (Downward Facing Dog) and prepares us to do other inverted poses.
Make sure your legs are "poker straight" and your hips are above your heels to protect your back.
Start with your chest in a concave position and use blocks as necessary. Or, if you have lower back issues, try the pose using a wall or a counter top.
Bring your head down and use support as needed: blocks for the hands, block for the head or simply hold your forearms.
I was told by a teacher of foremost authority that something "special" happens after you stay for 30 minutes but I have only made it to 22 so far! " The Sanskrit word "Uttan" also means "flying up".