I’ve resigned before. All you really need is a nicely typed and laid-out letter stating that you will be resigning from your job, and that your last day of work will be [specific date]. You hand this either to your immediate supervisor, if they have hiring/firing power, or the “big boss” of your section, etc. No reason is necessary.

If this is coming out of the blue, from their perspective, be prepared for lots of questions. Answer honestly, but politely; circumspectly or fuzzily if you need their good recommendation in the future. If they suspected it was coming, or aren’t surprised, then expect a short, perfunctory good-bye session.

Of course, not knowing your specific situation, there’s not a lot else to say. Good luck!