Financial aid from the government is almost completely loans. Unlike undergraduates who can rely on a certain amount of grant-based aid, grad students do not have that available (that I know of).
If you can get the subsidized loans, the government will pay the interest while you're going to school, and you can hopefully pay back all the principle soon after graduation when you get the job that made all the work worthwhile.

Some schools have internal grants available for grad students.

Depending on your department and program, you could get supported on a TA or RA (research assistant). Your best bet is to find a professor who has (or can apply for) a grant for some specific research that you can do and get supported.

Finally, there are a number of extra-curricular grants available through various agencies for grad students (NSF and DOD for example).