OP, it goes something like this: Your parents fill out the FAFSA and any other diagnostic test tools the school chooses (likely the CSS). This diagnostic tool is used to determine the parent’s contribution and the Student’s contribution based on income, savings, assets, number of children in school, age of parents, and other factors.
The school determines the total cost of attendance at their school. This number includes spending money for going out, rent, meal plan, books, supplies, incidentals, transportation- everything, based on a frugal student getting by for the year. This is called the cost of attendance or COA.
Some schools, including the “great schools” many aspire to, agree to meet the demonstrated need of every student they admit. That means that the budget that they propose will cover the full COA.
The budget they propose will consist first of the Parent and Student contribution. The student contribution will typically include imputed income from term-time work (work-study) and summer job income. Next will be loans TO THE STUDENT. These federally guaranteed loans are limited to $5k - $7k per year and index up each year. I forget the exact amount, but others will come to the rescue, I am sure! So total student loan debt will be limited to about $25K for a typical 4-year undergraduate degree- probably less than a new-car loan, except student loans carry a longer term to pay them off (but they also have a higher interest rate).
Some schools give financial aid that does not include loans in this COA budget, so their students graduate debt-free. Some schools do not guarantee to meet full need, there will be a gap between their proposed budget and the COA, which will need to be covered somehow- like with private loans. Most of the “great schools” you hear about do not do this- they meet full need and do not ‘gap’ you- though state flagships and schools with smaller endowments may not be able to meet full need.
After parent contribution and student contribution (as determined by a tool like FAFSA or CSS) and loans (if any), then schools add in Federal Grant aid (basically Pell grant if you qualify), State Grant aid (if any), outside scholarships, and institutional grant aid, often in that order. However, some schools will allow outside scholarships to displace loans before displacing institutional grant aid.
Moral: Outside scholarships are good to replace loans (even with full financial aid) but parent contribution is the last item to be displaced. It is not likely that you will get in over your head in loans if you are an excellent student just trying to get an education, and your parents cooperate and pay what the colleges think they should. Uncooperative parents, parents with complicated taxes, and parents with a lot of unsecured consumer debt will be in a squeeze. “Typical” parents (if that is even a “thing” anymore) should be able to get a fair shake from the schools.