Please clarify some magic stuff, Some questions I've been wondering about Options

[Gray Vagabond]

I'm new at this Shadowrun stuff and GMing, and I've had a few questions about magic things. I hope I can ask all of them in this post and not have to bother everyone after this, but... Here goes.

First, the Shamanic Mask. The only thing the RAW says about it is that some magical traditions have it, and it makes it easier for others to notice that the mage is casting spells. (+2 dice to perception test). What determines whether or not your mage has a shamanic mask -- is it just possessing a mentor spirit? Is the shamanic mask then just a disadvantage built into having a mentor spirit?

Then I have a question about the Heal spell. It says the Drain value is (Damage Value) -2. What is the Damage Value, is it the number of boxes of Physical damage the target has taken? Or is it the number of boxes the mage is trying to heal? Since you use the Drain value to determine how long you must concentrate to make the healing permanent, it could make a big difference.

Thanks for all help you can provide.