Free Application for Federal Student (FAFSA) is a form that you must fill out if you're looking for federal aid at any school across the country. Typically, you will work on it in early January of your senior year of high school. College Scholarship Service Profile (CSS) is for institutions that want additional information because they are going to be using more of their own aid dollars instead of taking money from the federal program. So they might want to look at, for example, the equity in your home and your assets.
You should fill out both, the FAFSA and CSS profiles; even if you think that you make so much money that you do not need to apply. There have been many incidences when families did not apply just because they though they would not qualify. Take your time to understand and investigate. For the amount of time to fill out the federal form, it may be daunting, but for that short amount of time to fill that out, you may receive a lot of aid, which makes the entire process worth it.
Often families put barriers on their children, restricting them to apply to only certain schools because of its tuition fee which they think falls within their financial range. That's probably not a good idea because what you should be looking at is that it may in fact be cheaper for you to go to a school based on their aid policy than another school which initial price is less, and it may increase over the years.
Nationally, for the past 3-4 years, many institutions are redefining at how they look at financial aid and how they distribute their aid. So there are many programs that are based on different aspects of your finances. Some are based on the level of income where you pay a certain percentage of the tuition. And if you make a certain amount of money, other programs may not offer you need based loan, but they can offer you money in form of grants.
You should direct any questions you have regarding financial aid to the financial aid office, because if you do not they simply can not help you.