To add a new task to the Task List, click on New Task in the toolbar.

This throws up a window in which you can enter all the details of the new task. Press OK to complete it.
The default values for the properties of a new task are based on the current task you have selected.
To complete a task, click on the "completed" box for the task, on the Task List.
To remove a task without completing it, click on 'Delete Task' in the toolbar, or use Ctrl+Del as a keyboard shortcut. You can select a number of tasks and delete them all in one go.
To delete all completed tasks, choose Edit->'Delete all completed tasks' in the main menu.
To change any property of a task, click it in the Task List and change it there. Or double-click the task, or press F4, and the Task Properties window pops up, for you to make your changes.
To change the same property in several tasks at once, select the tasks then press F4. You can't give all the the tasks the same title, or the same note.
To hide a task, set its priority to Negative. Then the task will be hidden unless you have opted to view negative priority tasks. To do this, choose View->Show Negative Priority.