Very simple. School interview, wear a suit. When you visit the site for an interview, business casual, with a tie. Everyday working day, business casual, unless you are requested to wear a tie for a presentation to upper management or somethng. Some places have special casual dresss days where they are allowed to wear jeans etc.
Good luck in your career. I just finished mine 39 yrs. in the nuclear industry. Its come a long ways and I was involved in all of it. Been lots of fun. First worked with one of the NSSS makers then took a job with a nuclear utility back in the late 70's and stayed until I retired.