How does a newbie get a bike?
I'll try to shorten the story. As a note, I'm a 16 year old male who is about 5'3" (short, yes). I needed a bicycle eventually for urban riding (point A to B, not highway commute) but I'd much rather ride than use a car (gas too expensive) so I might use it more often than I thought. I looked for a bicycle in shops over two weekends, but after the inability to find any agreeable bicycle (we argued) my dad got so upset that I gave in and bought a Walmart Mongoose bicycle-shaped-object, knowing that it'd be terrible and was merely delaying the need for a real bicycle. Some of my problems as to why I didn't find a bike besides the fact that I'm a COMPLETE NEWBIE (so don't bash me please):
1. I didn't know where to buy. Most places were too expensive, or we just argued about something and couldn't pick.
2. I'm limited on a poor budget ($150-250). I have little money myself (no job) and even though my dad says he can spend any amount, I don't want to be greedy.
3. I'm short. I don't know how fitting works and if it can work on any bike.
4. I don't know what I'm looking for. A durable bike that will last years/decades? A cheap used bike that might not last long? What would justify my casual urban needs?
My question is whether I should keep the Mongoose and ride until it breaks, or return it and buy a different bike immediately. If I stick with Mongoose, I need to learn about getting a new bike in advance. If I should do the latter, how should I get a bike so I don't repeat my ordeal last time? Buy from a shop, online, or make it from scratch?
If I'm gonna buy from a store or online, am I forced to put in a large budget ($300-500, more?) to get a durable bike that fits me? Is making it from scratch the best/only way for me to assure fitting and durability at a cheaper price? But where would I find the parts and know how to assemble it?
If you guys have any other ideas, I'd like to learn about them. I know there's so much that a newbie is too oblivious about to make a good selection, but I'm trying to learn. Thanks for reading.