You may work on campus from your first semester without a separate permit:
Up to 20 hours a week while school is in session.
Full time during official breaks and summer, if you are enrolled for the next term.
The job must be at the school, or at a company that serves students on campus (a campus bookstore or cafeteria run by a company).
New students may start no earlier than 30 days before classes begin. The job ends when your studies end.
Before you start, ask your DSO. You will also need a Social Security number. See How to get an SSN: students, workers and spouses.
CPT (Curricular Practical Training) is work off campus that is part of your study: an internship, practicum or required work.
Get a job offer that fits your major.
Your school must approve it. Usually you must have studied full time for one academic year first (some graduate programs allow CPT right away).
The DSO adds the CPT to your I-20 with the employer and dates.
Work only for that employer, only in those dates.
CPT can be part time (20 hours or less) or full time. If you use 12 months or more of full-time CPT, you lose OPT. Part-time CPT does not count against OPT.
J-1 students may work on campus with permission from the RO (sponsor), usually up to 20 hours a week in the term. After study, J-1 students can use academic training. See F-1 OPT, STEM OPT and J-1 academic training.
M-1 students may not work on campus. Practical training is allowed only after the program, with USCIS approval.
Unpaid internships off campus can still need CPT.
Freelance, gig apps (Uber, DoorDash), tutoring for money, and online jobs for US clients are not allowed without authorization.
Paid work for a company at home while on F-1 is a gray area. Ask your DSO or an attorney before you do it.
Working 21 or 25 hours "just once". Track your hours.
Starting CPT before the I-20 shows it.
Working after graduation without OPT.