Sorry for the long delay to reply!
long story short is that every plus is a good lil thing and every minus is a problem.
- Say now that + means you get some of the spell, ++ gets you a lot of the spell, +++ most of it, and ++++ all of it (arbitrary values for the example).
- On the other hand say that - has you pick an effect from the exhaust list, -- makes you pick 2 effects from the exhaust list, and --- means your spell just puffs.
- you have a few dice and your final result is: + + + - x (x means blank). You have to distribute the + between effect and intensity. So you decide to throw ++ to effect and + to intensity.
- You still get a single mishap because of the - you rolled. But you can give up a + to dismiss that - so that you don't have to pick any mishaps from the exhaust table.
- Now resolve the spell.
That is the gist of it, I guess.