How to Write a Letter of Resignation
How you leave your current job is a statement of your character. Hand your letter to a real person in a courteous way. You never know when you might need a letter of recommendation, so be courteous and respectful!
If you want to resign immediately, then the letter only needs to be dated and signed by you, and consist of one sentence, "I hereby resign my position as (whatever position you hold) at (the company's name)." This record can then clarify potential salary disputes or liability issues after you are gone. You should also include your mailing address in case correspondence needs to be forwarded to you.
It can't get much easier. There is no need to explain anything.
Another "nice gesture" can be a sentence or two crediting anyone who may have served as a mentor. But don't use your resignation letter to vent frustrations or point fingers. Keep this in mind: Richard Nixon's letter of resignation was 11 words long. The shorter the better.
You're quitting your job and don't have a clue how to say it? It's easy if you remember that how you say it is a reflection on you - if you keep it brief and to the point, with maybe a positive note if you are indeed leaving on one, you'll go out the same way you came in - making a good impression.