There are two places where you can view tasks: the Dashboard and the "Tasks" page (from the main navigation menu).
View from the Dashboard:
View from the main navigation menu:
Your dashboard shows only "open" tasks (by default).
On the more detailed "Tasks" page, the default tasks listed are "Active" (only). If you choose "Closed" from the "Status" filter, you can view just "Closed" tasks. However, this does not change the setting that "Active" tasks are the default.
Marking a task as the status "Done" does not mark it as "closed." The task is still "open" even if it is "Done." A person who has been assigned a task can mark the task as "Done," but that still leaves it "open." Only the task creator can mark the task as "Closed." (A task can have multiple stages and each assigned user can mark theirs as "Done," but not all stages are complete. Once all stages are complete and marked as "Done," the creator can mark it as "Closed.")