If you decide to home educate your child and never send them to school, you don't need to inform anyone of your decision.
If you decide to remove your child from school to home educate him or her,you do need to contact the school and de-register your child. Go to Education Otherwise for a helpful downloadable document explaining how to do this.
Once your child has been de-registered you will receive a letter from Oxfordshire County Council with a form they would like to to complete. You do not need to complete the form and you are under no obligation to provide them with any information because they have no duty to monitor your child's education. The letter will also say that a Home Education Visitor will be in touch to arrange a visit to your home. Again, you are under no obligation to accept a visit and you can politely decline their offer of one.
People may tell you that you will be inspected and that you have to do 'lessons' and provide evidence of the work you are doing but this is not the case. There is clear guidance on Elective Home Education which describes what you must do and what you don't have to do as well as what the Local Authority (OCC) can and can't do.
Download a copy of the current EHE Guidelines for Local Authorities here