The homeschool law for what state you are in would determine where you start. think most states have a State Department of Education. Look your states up on the web and contact the area rep. My state's area rep. was able to guide me through what I needed to do and filled me in on how to deal with the local county school district if they tried to require more then the state requires.
Someone below posted this link: http://www.hslda.org/laws/ and that is what I was going to post. One of the first things you might want to understand about homeschooling is that you ARE NOT IN PUBLIC SCHOOL now. Public school friends will see you as the enemy as a general rule, because you are saying by your actions that public school is not acceptable.
Another thing...if you are going to homeschool, and need help getting started, ask another homeschool mother who has been doing it for a few years for help. Certified or degreed teachers know nothing about homeschooling; all they know is how to do classroom management and how to take something exciting and interesting and make it DULL DULL DULL and meaningless.