I need advice on choosing a bike?

I decided a few months ago that fifteen is way too old to not know how to ride a bike so i decided that i was going to learn how to ride a bike as a form of exercise and transportation. So my mum took me to a place where i could rent a bike for a few hours to learn the basics and i did pretty well, i almost have my balance taken care of, and my best friend taught me how to properly use the brake, but i'm afraid to put my feet on the pedals (i learned kinda backwards) and even though i know that i should grip the brakes gently i get really nervous and squeeze them too hard other than that my mum says that i'm just about ready to get a bike of my own to practice with. But the problem is i don't know how to shop for a bike. i've read that i have to judge what ind of bike i'm getting by my height, where i'm planning to use the bike, and how much i'm planning to spend. I umed that would make it easier to choose one but i still don't know what kind of bike there are or what kind of bikes would be best for someone in my situation. according to my mum our budget is low so we're just going to Take our chances on craigslist but there are a lot of options and i don't know what to narrow it down to. So What kind of bike should i get? I'm 5'2 and i just want to use it around the nieghborhood.