Closure Contains Two Main Functionality like Retrospective and Acceptance.
Retrospective can be done on closed sprints or current sprint and it can be start and stop.retrospectives is to ask questions to the Scrum team, and collect and cluster the answers.
Acceptance shows a list of all Closed Story. Acceptance is useful for accept or reject the closed story and if a person who has permission of acceptance is allowed to re-open the story as well.