I'm a substitute teacher in VA (and I see you've gotten some responses on what we need here) Other posters are right - just call HR for the school district you want to teach in. You're going to have to call them anyway to see what kind of paperwork, etc. that you'll need to give them.
Just FYI - I LOVE substituting! I was a high school teacher before I had children, then I stayed home with them until my youngest was in kindergarten. Now it's hard for me to go back full time b/c of my husband's schedule, so I only sub at my girls' school. I bring them to school with me in the morning, and bring them home at the end of the day. It's awesome. And, once you've been in a school for a little bit and get to know the teachers they will be calling you ahead of time to request you. JessinTexas is right, the phone does ring awfully early. But once I was at my daughters' school for a couple months the calls started coming directly from the teachers. I guessing about 99% of my jobs are prearranged now (which is soooooo great b/c then I know when I'm working and I don't have to take a 5am call!!) I work about 2-3 per week by choice. I could work every single day if I wanted to. Hopefully you'll like it as much as I do. It's pretty decent money - about $100/day here. For a job that is this convenient, that's not bad!
Oh, the only bad thing - I actually have a master's degree in education but I don't get paid any more than someone with a bachelor's :(