While you wait for interview offers and decisions, you can complete and submit your FAFSA application, which opens on October 1st each year. It's best to submit your FAFSA application early, rather than waiting until you receive an acceptance. (In fact, if you end up on a waitlist, you may not receive an acceptance until after the FAFSA filing deadline, so simply take care of this step in advance.)
The AAMC's Financial Aid Application Process webpage explains how to get started. (Note: this page is written for medical school applicants, but their advice applies equally well to all professional school applicants.) You must list at least one school in order to submit the FAFSA application, but you can log back in later to add more schools. We recommend listing your in-state public school when you submit your FAFSA early; they will automatically receive information from FAFSA but will not process it unless/until you enroll in their program.
Pro Tip: In the section where it asks if you will be living on-campus or off-campus, select off-campus. This selection is not binding, but off-campus students are eligible for more financial aid due to greater costs associated with transportation and meals.