To set task completion enter required completion value in "Complete" entry field using up-down buttons in "New Task" dialog.
Alternatively, enter required completion value using keyboard.
To change task completion value open "Edit Task" dialog of the required task, open and repeat the actions mentioned above.
When task completion value is changed from ‘0’ to ‘1’, this day date appears in the “Date started” column
When task status is changed to “Completed”, its finish date automatically appears in the “Date completed” column.