Here are ways to create to-do items:
In a note you create or receive, or in a message you receive, select the text you want to track as a to-do item and click To Do in the toolbar. Or Control-click the text and choose Add To Do from the shortcut menu.
To change the item’s title or add more text, click in the field and start typing. The original text remains unchanged in a note or message you received; in a note you created, the original text is updated with your changes.
To set options such as a due date, alarm, or priority status, or to add the item to one of your iCal calendars, click the Details arrow to the left of the to-do item.
To highlight the original text in the note or message that you used to create the item, select the down arrow to the right of the item.
When you think of something you want to track, click To Do in the toolbar and then enter information about the to-do item.