Laws vary state-by-state. Link here for US State guides.
For Virginia parents: (My State)
1. The Notice of Intent to Homeschool: Printable NOI pdf from HEAV.org This is a document parents submit to the school system at the beginning of each school year, with details on courses your child will be taking during the year. Then, at the end of the school year, a second form is submitted noting completion and grade assessment. Information on curriculum details can be found here. For the NOI submissions a parent needs either: 1) A high school diploma, minimum; 2) A Virginia teacher’s license; or 3) Show you can provide your child with a curriculum/program for home study (example: curriculum you have purchased); or 4) Proof of your own ability to provide an adequate education. Note, August 15 is the “cutoff” date for submitting these BUT my first child to be homeschooled was pulled out mid-year. I used this NOI mid-year with no problems.
2. Homeschool with a religious exemption from the school system. This is for parents who hold a sincere religious conviction and want to opt permanently out of the public school system. This option has to be considered carefully as it is permanent removal and is very difficult to put children back into the school system later. It is however, my personal choice as it does remove the government from exerting itself over a child. Please begin reading here: HEAV: exemption from compulsory attendance. This article from their website is also helpful: The Law.
For other options and more information, I recommend you get acquainted with HEAV.org and consider joining the Homeschool Legal Defense Association: HSLDA.org A legal group that exists to maintain freedom in education. HSLDA requires a yearly subscription fee of approximately $120. Both organizations are invaluable resources for families who homeschool.