Keep it short and positive
A resignation letter has one job: to put on the record that you are leaving and when. The standard version fits on half a page in business-letter format: your name and the date at the top, your manager's name and the company, a greeting, a first paragraph stating that you are resigning from your position and giving your last day, an optional one-line reason, an offer to help with the transition, a thank-you, and a sign-off. That is it. The letter goes into your personnel file and may be seen during a future reference check, so it should read well years from now.
Do not vent. Complaints about pay, coworkers or management belong in an exit interview, if anywhere, and in writing they can only hurt you. If you are leaving because of a real problem, say "personal reasons" or nothing at all. The generator gives you a neutral reason menu, a formal or warm tone, a transition paragraph you can switch off, and an editable gratitude line, and it counts the days of notice between the letter date and your last day.
Two weeks' notice: custom, not law
Most US employment is at-will, meaning either side can end it at any time without notice. Two weeks is a professional courtesy that keeps references intact and gives your team time to plan, not a legal requirement. Two exceptions matter: an employment contract, offer letter or collective bargaining agreement may set a required notice period (30 days is common for senior roles), and some handbooks tie payout of unused vacation or eligibility for rehire to giving proper notice. Read those documents before you pick a date. Be aware that an employer can also accept your resignation immediately and walk you out the same day, which is common in sales and finance, so have your personal files out of the company laptop before you hand in the letter.
Timing your last day: most people resign on a Monday or Tuesday and set the last day for a Friday two weeks out. If you have a bonus, vesting date or benefits renewal coming up, check whether staying a few extra days is worth it, and remember that health insurance usually runs through the end of the month in which you leave.
Final paycheck and loose ends
When you get your last check depends on state law. California requires it within 72 hours of a resignation (immediately if you gave at least 72 hours' notice) and includes accrued vacation. Some states require payment by the next regular payday; others have no rule beyond the regular schedule. Unused PTO is paid out in California, Colorado, Illinois, Massachusetts and several other states, while elsewhere it depends on the written policy. Ask HR for a written summary of your final pay, benefits end date, COBRA options, and 401(k) rollover steps.
Before your last day, return equipment and get a receipt for it, save copies of pay stubs and performance reviews for your own records, and update your personal contact information so W-2 forms reach you. Deliver the letter in person or by email to your manager, copy HR, and keep a copy. None of this is legal advice; if a contract or non-compete is involved, a short consultation with an employment attorney is money well spent.