Re: What is the Soul/Spirit, and how do I attack it?
Well, I haven't actually played in quite a while, so I'm not up on the latest (I still have to pick up 5ed!). But no one else has attempted to answer your question, so I'll give it a stab.
First, what genre? Supers? Fantasy?
Second, it depends on what your GM rules. Oddhat did a great thread in the Champions genre forum about the New Circle, a group of superheroes who are specialized to fight evil spirits. He did all of his spirit attacking stuff with Affects Desolid--All Forms. But that means that his GM would have ruled that spirits are a form of desolid. So ask your GM.
I have a very old "Hero Almanac", third edition rules I think. It says that to affect spirits, you need to buy a power with advantages: Affects Spirits (+1/2), and Based on EGO (+1/2), for a total of +1. I think +1 is the same cost as Affects Desolid--All Forms, but I'd have to look it up to be sure. Powers which already are based on EGO (Ego Attack, etc.) only have to buy the +1/2 Affects Spirits advantage. I don't know if these rules are still canon, as they are quite old. There are other powers which affect spirits directly, such as Shift Spirit (used for "soul jar" powers as well as excorisms), Spirit Summoning, Consume Spirit, etc.
Anywoo, that should give you an idea of the total point cost for affecting spirits. Check with your GM, or if you are the GM, you should charge about +1 on normal powers to affect spirits, and about +1/2 for powers based on EGO. You might want to ask around for where the spirit rules are now (they seemed Fantasy oriented in the Almanac). Check the FAQ too, there might be some hints in there.
Good luck!