The ideal bike is a rental bike so you don't have to worry about dinging it.
DFox was right on, take it in stages:
1. walk bike slowly and practice braking
2. coast downhill with no pedals, or feet outstretched to learn steering
3. start adding pedaling, do not put both feet on bike before moving. If the bike's not moving you'll fall.
4. celebrate
5. try shifting between 2 gears WHILE pedaling
6. celebrate
7. repeat any of the above you want to practice on more
8. try riding on empty bike trails/roads
9. when have balancing and shifting and braking review bike safety rule for road travel
10. get on the road and practice more
11. celebrate, you've made it.
good luck, let us know where you get stuck. kudo's to you for taking this leap.