The most common usage of "P.S." is when an another part/correction has to be added to already written and signed letter.
For example:
Dear abc,Letter Content. Letter Content. Letter Content. Letter Content.Yours sincerely,Alex RadyushinP.S. Here goes ps part.
P.S. stands for Postscript. P.S. is an initialism (type of abbreviation which is pronounced letter by letter).
It has Latin origins from "Post Scriptum" (translated as ?after the main script?).
If another part has to be added after P.S., P.P.S. is used and so on...
