Dear [Manager's Name],
Please accept this letter as formal notice of my intention to resign as [job title] from [company name]. My last day will be [date of last day] in accordance with my notice period.
I'd like to take this opportunity to express my gratitude for the opportunity to have worked in the position for the past [time in employment]. During my time here, I've learned a lot and enjoyed working with my colleagues. I will take much of what I have learned with me into my future career and regard my time here as a valuable period in my professional life.
During the next [notice period in weeks], I will do everything I can to make the transition as smooth as possible, and I will assist in any way I can in handing over my responsibilities to colleagues or my replacement. Please let me know if there is anything else I can do to help with this process.
Sincerely,
[Your Name]