How to Mark Tasks "Completed"
When you have finished a task on your list, you can click the circle icon next to the task title to mark it complete.
After you task is completed, it's not gone! You can view all of your completed tasks by pressing the "Done" button (which will also display the number of completed tasks).
Tasks that are completed will have a green checkmark next to them, and the task title will have a strikethrough.