Generally speaking, what happens to someone who files for bankruptcy?

What's the difference between chapters 7 and 13? I know for a fact a person's crredit takes a major anal raping. This I know, but what else happens to them? Example: Let's say a person is sued by a hospital for not paying their bills. They have no income or not enough to pay off the debt, so they file for bankruptcy. What chapter would they file this under?