To get to the Tasks section of the Master Tour desktop application, just click a Tour Date on the right side, then click the Tasks and Notes section on the left side. You can also click Navigate>Tasks Notes in the top menu bar, use the Cmd-6 keyboard shortcut on MacOS, or use the Ctrl-6 keyboard shortcut on Windows.
To add a task, click the + Add button shown here:
Then enter the Title of the Task, any Details you need, and set any Due Date and Visibility you might need. If you want to know more about the Visibility feature, check out this article on Visibility.
Due Dates are set by clicking on the calendar icon then selecting a Date from the monthly calendar, and Due Times are set by clicking on the clock icon then selecting a Time from the dropdown list of times. You can also manually type in Dates and Times, but only in the same format shown in the Due field (varies depending on your computer's date and time settings).
If a Task is past its Due Date and Time, it'll appear as Overdue in the desktop app, with red text and "OVERDUE" at the end of the title:
To mark a Task as complete, click on the checkbox to the left of the Task's title. It will then check the checkbox and make the Task Title appear with a strikethru text style.
To delete a Task, click on the trashcan icon to the right of the Task's title, then click the "Delete" text to confirm the deletion.