I-502 Fact Sheets from WA State and ACLU of WA
Though the law goes into effect on December 6, it is December of next year when the licensing system for sellers is scheduled for. (If you think that's a long time, don't ask me how long we've waited for Washington, DC to get its medical marijuana law moving.) An evaluation is to be published in September 2015. (Which is as long as DC is taking to just get started.)
502 does not provide for home growing. But patients maintain their home growing rights under the state's medical marijuana law.