Education taxes in the United States can seem complicated, especially since the standard tax forms and publications aren't the easiest to navigate, and often schools and employers don’t provide general help even when the majority of their students will have very similar situations.
If you keep the basic concept of an income tax in mind, though, it should become easier to figure out:
Any and all money you receive from someone else is taxable and must be reported as such unless otherwise specified1.
I will go through the 4 most common income categories for a graduate student, with the assumption that that the reader has never filed taxes before, and provide information on free tax filing programs.
Disclaimer: I have no formal tax training. I’m just a moderately intelligent graduate student who has dealt with this for a few years and read the relevant documents.