First of all, I’m not in the US so I can’t say anything about how it works there, I only know the rules that applied to me (I live in a small European country).

If you can’t afford to pay your monthly payment, you submit an income statement. If they agree you make too little then they either lower the monthly amount or don’t have to pay at all, depending on income. If your income increases you have to start paying again. The payments (if you can afford it) are so that the loan is paid back in 15 years. After 15 years whatever is left of your balance is forgiven. The loan also had a 0% interest rate. Also, part of the loan would be converted into a gift if you managed to graduate within a certain time frame.