In a nutshell, the first thing that you will need to do is draft your Articles of Incorporation and file them with the state. A quick search on google could probably give you examples of how to write them. You would file with the application that can be found here
. In addition, be sure to check out http://www.ss.ca.gov/business
Note... filing this does not entitle you to tax exempt status. You will need to fill out the proper IRS forms. For a list of requirements for that, check out this link.
As far as how a booster organization operates... your best source of knowledge will be to actually attend a booster meeting or two at another school.