An Azar ID is a unique identifier located on your profile, under your nickname, and that can only be seen by you. It can be used to add your friends by going to the 'Message' tab > 'All' Friends > tapping on the '+' icon at the top of the screen > select 'Add friends by Azar ID'.
You can make an Azar ID by clicking on the Azar ID icon located next to your nickname on your profile page. Please be advised that you cannot change it once it's been set.