First you need to register and link your BlinkStick to this website. Find out how to do this here:
Enable public access for your BlinkStick and you will see "Public" section in the device details page. Your LED will have a public page and you can share it to Twitter, Facebook and Google Plus using the button or just posting the public URL anywhere on the Internet. The QR code contains the URL encoded for devices which have barcode scanner application.
Visiting the URL will let anybody change the color of your BlinkStick when it is online.