Great! You've come to the right place!
Now what? Right?
First of all, don't panic. Don't overwhelm yourself reading everything on the internet. Read a section of this website at a time. Take some time to digest. You don't have to figure it all out in one day. Yes, even if you just pulled your child out of school. Really, Give yourself a little time to get organized. It will be OK.
So let's start with the number one thing you should know: In the U.S., homeschooling is legal in all 50 states. If you live in another country, that might not be the case. If you do live in the United States, you will want to visit this page to get more information about your state's requirements. It is very important that you follow the laws where homeschooling is concerned. I'd like to tell you that if you follow the laws, you won't have any trouble. However, we know that all it takes is one nosy neighbor or disgruntled relative to get you in hot water. That is why joining a homeschool organization is a good idea. The page I linked to for the state laws is from Homeschool Legal Defense. Yep, you guessed it. If you have any trouble with people accusing you of doing wrong by homeschooling, they will come to your aid. Membership information is on their site. There are also various state organizations who provide the same services and more. You can look into those. It is not a requirement to join, but it gives some families peace of mind. Now our family has never had a problem in 14 years of homeschooling, but I think of it as insurance--there if you need it.
Some states require that you file a notice of intent to homeschool. It's really as simple as filling out some paperwork and getting it sent in by a certain deadline. Other states require you register your homeschool under an umbrella school. Some states ask that you register as a private school. You might have to choose a name for your school. Have fun with that! There are some great homeschool names out there. Testing is sometimes required. Certain states have teacher qualifications that must be met. A list of required subjects are sometimes given. You will find it varies from state to state but remember, homeschooling IS legal in all 50 states.
First task: Check the laws in your state to be sure your homeschool will meet all of the requirements before you begin.