I have noticed some of the postings have a mark in the bottom stating it have been edited.
Oh have I missed that many times, where i see typos or misspelled words.
Reading the "Getting started" says nothing about editing posts. Neither do "Formatting" - so what is the magical formula?
Click at your User Profile up or down to the right - you'll find your latest postings there and can edit for 30 minutes, I think, or as long as you see a yellow pen icon. You'll have to write your login and password twice, though.