On the Home tab, click Categorize, then click Edit Categories. Modify Existing Categories or Create New Categories
If you are not seeing the category you would like, you will need to create a new category. By default, the item list is displayed vertically between the navigation pane and the reading pane.). You can assign an item to a standard category, such as Family or Travel, or to a category that you create. Because categories are color-coded, when you view the item list, it's easy to see which items belong to which category. You can organize your messages, events, contacts, and other items (items: Units of information in Outlook, such as e-mail messages, calendar events, contacts, tasks, and notes.) by assigning them to categories.
