Although there are no guarantees, the department does its best to fund all of its graduate students through Graduate Teaching Fellowships (GTF’s). GTF’s receive a competitive compensation package that includes a monthly salary, full-time tuition waiver, mandatory fees subsidy, and health insurance premium coverage (and subsidized health insurance premium coverage for dependents).
Funding generally comes from either teaching in a departmental class or conducting research in a faculty’s research lab (or both). A student may bring in their own funding in the form of a scholarship, but that is more common for advanced PhD students. Note that a student must be working in a faculty research lab in order to be eligible for either a research or teaching – there is no “classroom only” option.
More details about the GTF mechanism can be found on the graduate school’s website.