Part time Work & Work Permit
It is allowed while one studies, though there is no minimum wage system. There is no permit required if a student works 'on-campus' but only for 20 hours a week. If one works outside the campus, say on internship, the student has to obtain a permit called 'CPT'(Curricular Practical Training) and can work for 40 hours a week.
If the student works outside, not as part of his/her course, he/she has to get a permit called OPT (Optional Practical Training). OPT also gives the option of working one more year in USA after completion of the studies.