Goodman Games

What can and can't level 0 characters do? Can they cast spells if they find a scroll for example?

I would use the text from page 106 about untrained classes and spells/scrolls as a guide ("Spell checks by other classes").

untrained spell check - d10 with no mods.

The rules are good guidelines, but always remember that you are free to do whatever you want to enhance the story. I would advocate sticking to the rules pretty closely if you have little or no experience, but if you want to create a situation that requires a spell to be cast from a scroll in order to move the storyline forward, go for it. There's no reason that the party can't find a scroll that was prepared in a way that allows anyone to successfully cast the spell on any roll but a 1 on a d10, for example.

Page 21 has most of what you need for Zeroes.

Just remember the Funnel is sort of a sub-game, or game-within-a-game, in relation to 'leveled' play. I think the best, succinct description I've heard of it (and sorry, but I've forgotten who said it) was more or less "the Funnel is the ten minutes of the movie at the top, before the credits, where you don't yet know who the main characters are, and all hell is breaking loose...".