Ammo types

Hey guys! It's the noobie again, we'll one of us anyhow!

What's up with all the different ammo types and manufacturers? How do I know what I wanna get? Why shouldn't I just buy the super cheap 'reloaded' ammo and shoot wildly? If a single bullet doesn't have much stopping power 12 will right?

Why does there seem to be like 12 types of hollow points? Are there bullets that have stopping power and aren't as lethal? That last one sounds dumb considering the intent of the weapon but I still ask it.

What should I be looking for when purchasing 9mm ammo?