How do I begin and end an apology letter

Answer 1

Dear Sir (or Madam),
Sincerely yours,

Answer 2

Or

Dear ______,

Answer 3

Oh I meant the beginning and ending sentence..

Answer 4

Your beginning and ending sentences depend a lot on what you are apologizing for.

I'd start --

I'm so sorry about --

I'd end --

Please forgive me.