You will need a mountain bike with at least front shocks for the local trails. I recommend a Google search for "How to Choose a Bike", read all you can about the different types of bikes, then choose a local bike shop near you (Dirt Diva sponsors are the best place to start!) to talk with the personnel. You should be able to test ride a bike in the parking lot (bring your helmet if you have one), and the sales person should be interested in your skill level and type of riding you want to do. Don't buy a bike on the first visit, even if you like it. Come back to your Google search and see if there's anything else you need to consider (there is a lot out there), and possibly check at another bike shop, test ride another bike. A bike that fits you is going to be important to enjoying your riding. Your local bike shop should also provide warranty, initial fitting, first tune-up, and free advice.
You should expect that a decent (new) entry level bike will cost in the range of $800-$1000. It might seem like a lot, but cheaper bikes fail quickly, leaving you with nothing to ride!
You might also check on Craigslist and the Facebook Group "Charlotte Bike Market". Do remember, though, that a bike that does not fit you will not be comfortable and will get in the way of developing your skills.
Fall is a great time to get a bike and get riding!