This page describes how to mark a task as completed.
To mark a task as completed, do this:
On the Browse Tasks screen, scroll to highlight the task you want to mark completed.
Press MENU then select Mark Completed [ K].
A check mark now appears in the box to the left of the task title.
If you change your mind about having completed a task, you can mark it as incomplete by highlighting the task, pressing MENU then selecting Mark Incomplete [ K].