Can F1 work as extern?

I'm currently studying nursing program for the first semester and have some clinical practice in the hospital. My classmate said the hospital can hire nursing student as nursing technician and nursing student can work part timely as extern ship. I'm a F1 student, can I work as extern as well? They will pay some bucks for the work, that's part of the reason I want to work. another reason is I can get a lot of experience while working in the hospital. Is extern illegal for F1 student? What's the difference between Extern and Intern and CPT and OPT? SOme wise man give some instruction plz. THx a lot