You can add a task in the following way:
Click the left mouse button in a blank part of the task list.
Type the description of the task.
Press Enter.
If you wish to specify attributes such as deadlines, priorities, notes etc. when adding a task then you should use the Task property sheet to add the task. You can add a new task via the Task property sheet in the following way:
Press the 
button in the shortcut bar in Diary Mode. The Task property sheet is displayed.
Enter description, deadline and priority information into the Details page. You can add rich text notes for the task from the Notes page.
Press OK to save your changes.