This article explains how to use My Work. The My Work feature is designed for Team Members, as a single page to view & update all work assignments. The Plan Owner will see the updated values when they look at the plan schedule and elsewhere (reports, etc.)
Navigate to My Work
Mark Complete
Select the check box to mark an item as complete. The field values will get a line through them. Status will update to Completed and % Done will update to 100%.

Update an Item In-Line
Update any field in line that's editable, such as % Done, Status, etc.

Field Calculations
Some fields are auto-updated based on the values of others, such as the Complete Check Box, Status, & % Done. If you update the Status from Not Started to In Progress, the % Done goes from 0% to 50%, and vice versa.