Schools use this info in different ways. Ultimately, the Certification of Finances is needed in order for you to get your Student Visa. You need to show verification for all the money that you can get to pay the cost of attendence of going to your college here in the US> You fill out everything you can pay from all sources (family, government, savings, sponsorship, awards, etc) and it has to all be verified, and the college fills in the rest if they choose to give you that amount.
Some schools will give you your financial aid, merit award first, and then you fill out this form to come up with the amount you need to make going to that school possible. If you need $60K to cover you for a year of study at a college, and the college gives you $20K, you have to come up with $40K on that form with certification that the funds are there and available for you in order for US Immigration to issue you a Student visa.
Some schools want this Certification up front as it forces the student and family to come up with a figure that they are willing to pay and proof that they can pay it. The school then can look at this amount of money along with the financial aid application, and use both sets of info to come up with an award. It serves as verification of your financial information and also gives the school an amount that you/your family are committing to put towards the cost of college. . Exactly how each college uses this information is up to the individual school. If your financial need by formula from info from your fin aid statement shows that your expected contribution is $20K, for example, but you can only come up with $10K on the Certification of Finances, you have a gap , and for need aware schools, it might be reason to turn you down since you are certifying that you cannot pay what it costs to come that college. Whether the school will discuss this with you further or just offer you the amount that they calculate as need and let you deal with the form and how to get the extra money is up to the school. Or they may just reject you since you cannot pay, and they cannot come up with what you say you need in on that all important form.
Also if your expected calculation is say $10K, but you show on the Certification of FInances that you can pay $40K, or whatever–more than that $10K, it allows the school to adjust their aid to you to what you need, since you have additional sources that are reflected on the financial aid application.
It is not as easy for schools to verify info for many international students, so by having the student and family commit to what they are willing and able to pay, showing proof that they can pay it, makes for a process where there is more motivation to come up with the money on part of the family and student. However, it does make for a nerve wracking situation for the student.
In your case, it’s simple in that you put down what your family can pay out of various sources which is zero or nothing. I don’t think $400 is going to make a difference one way or the other. If Occidental or any other school wants you, they will have to pay pretty much all of the cost of your going there, which some schools will do, for those students they most want. As far as living expenses go, it doesn’t go by vague terms but by dollar amounts, How much in US dollars can you and your family pay towards your costs is what the school wants to know. With a financil statement showing an income of $9K a year, and if there are no assets or other sponsorship or awards, it’s pretty clear that your family cannot be expected to put more than a few hundred dollars toward your education. Hopefully, some school will come up with enough funds to make this possible for you.