For Redline Time Attack they don't really require any license or anything to my knowledge. Register at www.redlinetimeattack.com

For NASA, they require a license. You get this through HPDE I believe. As you work your way up you can become eligible for the license. OR if you have experience elsewhere you can see if they accept you. Same goes for SCCA time trials.

If you want to ROAD RACE, it's a different story. You will need a cage, a race seat, harness, fire, battery cutoff, and lots more. Some time trial series also require some of that, so READ THE RULE BOOKS.

Road Atlanta is a tough track, especially for beginners, you don't want to be out there for the first time in a group like NASA TT. There is open passing and they will pass you and come up on you so hard you will probably just quit lol. I suggest running the time attack October 3 at Little Talladega, or doing track days there first. Redline runs on some pretty safe tracks as well.

Look into doing NASA HPDE, they will give you an instructor and work your speed up, it's a great cheap way to learn without spending thousands on a racing school. Plus, you get to use your own car.

Check out:

www.redlinetimeattack.com
www.nasaproracing.com
www.atl-scca.org

SCCA has a PDX session at Road Atlanta for Atlanta Region events. It's like HPDE, just shorter, but only $100. They offer an instructor as well and you start in a beginner class and move up. Complete many of these and NASA will probably let you jump up a HPDE class or two depending on experience and logbook.

You get a logbook which says events you run, and your instructor signs it with notes or info on your driving.

Hope this helps, anymore questions just ask.