Asterisk 11.2.1 SUBCRIBE and NOTIFY

Hi everyone,
I have a Sipml5 phone running on google canary(27.0.1446.3) browser.
I am trying to find out how the SUBSCRIBE/NOTIFY mechanism in Asterisk 11.2.1 works.
How can we set status of a user from browser? (I am new to asterisk)
Anyone who knows how to set this up?