Melissa, you might want to look up a local bike club and see if anyone has a used MTB or hybrid for sale. You could start learning to ride on that, assuming it's an appropriate size, until you know more about what you need and want. You could also ask folks in the club about the various local shops--where to go, where to avoid. Clubs usually offer entry-level rides, so you can gain some experience and confidence on group rides with expereinced leaders. Lastly, shops or clubs often conduct basic maintenance classes, so you can learn how to change a flat, lube the chain--just real simple, basic things.

When you buy a bike, take into account several extras besides a helmet: a seat bag, spare tube, tire levers, a floor pump, maybe a frame pump. Even if you don't know how to fix a flat, you will likely get help, but you should at least have your own gear.

After that, the only thing still to do is enjoy your new hobby! And, by the way, you're not old enough to be "scared . . . about learning at my age."