I'm guessing that you got that aid package from a college that does not guarantee to meet 100% of students' documented financial need. Most colleges lack the funds to meet the full need of students, particularly students who are low income.
As to how people go to college: Many, particularly low income people, live at home and commute to 2-year or 4-year public colleges. Even high stat people may start at 2-year public college where they can get excellent merit aid, and later transfer to a local 4-year public university.
Some people also get money for college by taking out loans, working, taking time off and participating in Americorps (In addition to earning $200 or so a week, at the end of the year, you get $4,700 that you can use for college. You can do this for up to 2 years), or joining ROTC.
People also get money through outside merit aid. This is easiest to get through locally offered scholarships.
The majority of people have to take costs into consideration when considering what college they can go to.
You have other choices beside working at McDonalds for the rest of your life because you apparently can't afford your first choice college.