The platform of the pillory, or the scaffold, is an actual platform that a guilty person must stand on for a length of time in order to be put on display for their sins and suffer public humiliation.
who: Hester and (baby) Pearl.
reason: Hester's punishment as dictated by the laws of the colony for comitting adultery
significant spectators: the entire colony, the magistrates and ministers, Chillingworth (who has just arrived)
outcome: Hester will not reveal who the father of the baby is, even when persuaded by Dimmesdale himself (sit. irony); Hester shows no signs of remorse nor fear - looks very proud.
who: Dimmesdale then Hester and Pearl with him
when: middle of the night about 7 years later
reasons: Dimmesdale seeks resolution and forgiveness for hiding his secret sin; in this symbolic act of repentance (in front of no one) he believes this will provide his soul with relief
significant spectators: no one, but Chillingworth shows up at the very end and it is a mystery how long he's been there and how much he has seen
outcome: Pearl and Hester join Dimmesdale and for a moment he has an unusual feeling of strength; Pearl asks him, "Will you stand with us, we three together, tommorrow noon-tide?" She continues to condemn him for keeping the secret; a shooting star then bursts through the sky leaving what looks like a large letter "A" behind it; the next morning the townspeople who saw it say it was an A for "angel" as the great Gov. Winthrop died the night before; also, Dimmesdale forgets his glove on the steps, and when it is found the next morning the townspeople say that Satan himself must have taken it and placed it there.
who: Dimmesdale, Pearl, Hester
when: middle of the day, just after the annual election day speech made by Dimmesdale
reason: Hester and Dimmesdale plan to board a boat and leave for England; this is Dimmesdale's final action to absolve himself of his sin; he climbs the steps first then encourages Hester and Pearl to join him
significant spectators: the entire colony plus a bunch of visitors
outcome: Dimmesdale rips his shirt off and although it is not said exactly what is there, it is assumed he has his own scarlet letter on his chest; the entire colony finally knows the truth of who the father is; Chillingworth approaches the steps and tries to get Dimmesdale to come down, then says, basically, this is the one and only place you could have escaped me - confirming that the only way for Dimmesdale to truly repent was to come clean before the people; oh yes, and Dimmesdale dies.
'pillory' is it not?