Final answer:
In Outlook, once a task is marked as complete, it is moved from the To-Do list to the Completed list, helping users track finished tasks.
Step-by-step explanation:
When you mark a task as complete in Outlook, it is removed from the To-Do list and placed in the Completed list. This allows you to keep track of the tasks that you have finished without cluttering your active To-Do list. Tasks in the Completed list will show strike-through text indicating that they are done, and you can review them at any time to keep track of your accomplishments.