These are the three easy steps involved in officially home schooling a child. Please note that this is a guideline for my home state of NY. I have no idea what other state laws mandate as far as enrollment, documentation, and testing go, but I imagine that it falls along these lines. Please also be aware that a person "graduating" from a home school program won't necessarily have an official diploma unless you follow steps beyond what's listed here.
1) Submit a letter of intent to your school district's superintendent. It should include the names and ages of the children whom you are going to home school and the years for which the schooling will take place. A new letter must be submitted prior to the start of each school year. You do not need to submit the first letter until the school year during which your child will be turning six-years-old (though it wouldn't hurt to make it official with the school district if you choose to begin Kindergarten before the age of 6). After your child has turned 16-years-old, you do not need to submit any more letters (though it also wouldn't hurt to keep everything recorded until graduation).
2) Choose your method of madness: i.e. what textbooks and curriculum's will you be using? One should really begin to think about this and explore options well before the beginning of the school year. I would suggest the following: 1) Order a paper homeschooling catalogue from http://www.christianbook.com/ or go online where you can see a variety of different options all in the same place. 2) Find other HS families in your area and ask them what they use (churches, libraries, and the Internet are great ways to find local groups). 3) Attend a used curriculum fair. There's a 2-day one about 20-minutes from where I live now and it's a huge event! Larger cities usually hold them annually.
3) Submit a quarterly report to the school district. It should include the child's name, address, dates for beginning and ending the quarter, and the child's grade level. List each subject by name, and then include highlights of what you've done as well as a letter grade. For example:
Math: Jenny completed units 1-9 of Scott Forseman Math, Grade 2; included were the concepts of basic addition and subtraction through numeral and word problems. Grade: A-
http://www.thehomeschoolmom.com/ Find out about laws, regulations, and resources by STATE in the US
http://donnayoung.org/index.htm Schooling and education ideas and resources
http://www.homeschoolreviews.com/default.aspx Reviews of almost every home school curriculum out there!
http://www.christianbook.com/homeschool Allows you to view and purchase different curriculum's (note: though owned by a "Christian" company, the educational materials provided are not necessarily "Christian")