And now we're to the thorn in my development side, always. Magic. I can usually get cyberware and general physical conflict worked out with a little tinkering, and then toss in adept powers for good measure, but sorcery and conjuring always gives me headaches. If ever there was a mechanic where I'd want to invoke this system's name, this would be it.
Even throwing away most the details, it still winds up more complicated. So here's the breakdown:
Magical activities are qualities. You want to perceive something astrally? Roll your Assensing quality. You want to engage in astral combat? That would be Astral Projection. Each spell is it's own quality too. So is summoning and banishing. Yes, that's a little rough, but you get free qualities for being a mage the same as you get free cyberware for being a sam, and in my experience mages in SR only cast a handful of spells anyway.
Whenever you cast a spell, you roll the appropriate spell quality. The GM also rolls the spell quality, with a TN set at your Runner Type, or spellcaster quality, whichever is more appropriate. Any successes on the GM's roll turns into drain damage, which are downshifts, not actual damage. You can allocate any successes you get on your roll to offset this damage. Anything you don't spend there applies to your spell effect.
Summoning works similarly to spellcasting: roll your summoning quality opposed by the GM's roll. However, this time you choose the TN for your roll, and the GM gets the appropriate bonus. Thus, if you choose an Average  roll, the GM gets 2d6 + 0, and your TN is a 7. You may allocate any successes to drop this drain as normal.
If you succeed, you summon the spirit. It has a number of qualities equal to the TN of your roll. Thus, an Average spirit would have 7 qualities. You can assign them to whatever seems appropriate to the spirit type. Any additional successes over what you needed to summon the spirit gives you an additional service; base summoning gives you only one.
Banishing is a straight up combat roll opposed by the spirit. If the spirit wins the exchange, it causes damage in the form of drain. If the banisher wins, he reduces the services the spirit owes or, in the case of free spirits, reduces its qualities as per normal damage.