How do I search and read stories that are already Done?
What do you mean by "user stories which are done"? Do you mean "accepted"?
The user story's state is stored in the ScheduleState field.
You can use either the Plan -> User Stories to filter by the ScheduleState (and choose 'Accepted') or you can also choose the Plan -> Work Views page where you can choose the project/s then choose to display user stories and then include a similar filter on ScheduleState.
Please let us know if that helped.