When you apply for admission, you are NOT applying for financial aid. These are two distinct procedures. If you are accepted to a school, enroll and do nothing else, you will NOT receive any assistance.
To be considered for financial aid, you must (at minimum) complete a FAFSA (Free Application for Federal Student Aid). You'll fill out the paperwork after January of your senior year. On your FAFSA, you'll indicate those schools with whom you want to share the results. Only after you are accepted will the financial aid office examine your FAFSA results and build an award package to (hopefully) meet your need.
Again, if you have not submitted a FAFSA or have not sent the results to a school that accepts you, their financial aid office will do nothing.
Don't let this happen to you! Know which forms are required for each school to which you intend to apply. Many selective schools require additional paperwork (CSS Profile and/or their own customized form). Promptly complete and submit all the required forms and if necessary, follow up with the schools as to your status.