The columns on the Stories page represent all the workflow states in the Workspace as defined in the Workflow section of your Shortcut settings.
Point totals for visible Stories in any given column are listed at the top of that column and further information can be gathered by hovering over that number.
You may choose to create a Space for yourself and/or your co-workers that hides certain Workflow States you don't want to see. You can hide them by going to the column's settings menu (the dropdown menu) and selecting Hide Column.
To unhide columns, click on "Everything" under your Spaces in the sidebar of the Stories page and all columns should re-appear.
By default, all Stories in "Done" columns are ordered by the date the stories were moved into the column and the columns are divided by week starting on the Sunday of the week.
Stories that were completed over 30 days ago will be hidden by default. You can load older content by clicking the Load Older Stories button at the bottom of the column.
More on Workflow State types here.