You may change your mind about how to homeschool once you get started, but if you're in an emergency situation, you need to choose something quickly to start with. There are a variety of options, depending on your finances and your goals.
Government Homeschooling:
I started out doing this. It means you stay in your school district but use the district's or state's homeschooling program. Most states have a program of some kind. Your child works at home, often on a computer these days. You oversee the work, but the government usually plans it, makes assignments, gives tests and grades, and decides how and what your child will learn. Sometimes you even meet with a teacher online. It's free, and usually doesn't require too much on your part, which can help in some situations.
This system works well if:
You don't really like lesson planning or teaching. (My programs allowed me a lot of freedom, but most don't, especially today, because they are usually online)
You are only going to have your child out a short time and want him to be in the right place when he returns to school.
You're comfortable with a government curriculum.
You're comfortable with the people you'd have to work with to do this.
You're comfortable being highly supervised.
This choice does not work well if:
Your child is behind or ahead in some areas and you want to use your homeschooling time to catch up a child who is behind or challenge an advanced child.
You want to control the learning experience.
You are uncomfortable with some of the teachings that would come into your home.
You're uncomfortable with the high level of supervision you'll receive.
There is one particular warning you need to be aware of:
Some homeschoolers are sort of snobby about government programs. They get offended if you call it homeschooling. (I am not among those.) Sometimes they won't let you join their groups if that's the method you choose. If you're counting on the support and socialization of the people in that category, you should be aware that you might not be treated nicely, so check with the group you were hoping to join to see how they feel about it. It's not that they should get to choose how you homeschool, but you will want to know how that will impact your plans.
If you're in a hurry, a government program is the very fastest way to get up and running and the easiest way to be sure your child will be at grade level when he returns to school. Ask your school district--not your school principal unless you think he would be supportive--to tell you about the options. If that doesn't work, call the State Board of Education. (Sometimes that doesn't work either--in one state we moved to, I called the state to ask how homeschooling works there and they put the janitor on because he homeschooled and was the only person who knew the answer.)