CalCannabis Cultivation is a division of the California Department of Food and Agriculture (CDFA). Over the course of the rule making process they’ve been able to assembled a very informative website page with all the information you would need to get started. You can find their website here.
You will also need to get approval from your local City or County. Generally your local authority will have a process as well. Hopefully they’ve assembled an informative website like the CDFA above. As an example see the City of Oakland’s here.
Recently they released a video of a presentation to help potential licensees through this process. You can find that video below. If the video doesn’t play you can find the original here.
If you’re looking for the California marijuana or medical cannabis rules you can find them here.