To cast a spell, the caster rolls a d20+ the caster's level. This sum is compared to the Spell's Difficulty (11+spell level). To successfully cast the spell, the caster's total must be equal to or higher than the Spell Difficulty total. If the caster's sum is under this number, the spell fails.
A spell successfully cast, can be cast again. Failure means the spell is forgotten and must be relearned before it can be cast again.
Casting a first level spell has a Spell difficulty of 12 (11+1st level spell), casting a second level spell has a Spell Difficulty of 13 and so on.
Currently its about 220 pages, but its a 6x9 digest sized book, single column pages. The artless PDF will be availble as a free download, the rules with art will be availble via lulu.com