Assigning a category to a file is a two-part process. First you assign the category, and then you define the order the item is displayed in that category

To assign the category

• Create or edit the article.
• Click on the plus (+) button on the right-hand side of the category field.
  This opens the Assign a Category screen
  
  
   
• Select a category by using the text entry field at the top of the screen. You can start typing a category name to filter the category list.
  You can select multiple categories.
• Click OK to save your changes and exit the Assign a Category screen.

On the Assign a Category screen you can also:

• Unassign categories from this article by clicking the x button.
• Drag and drop categories into your preferred assignment order.
• Select which category the article will be published in, and which categories the article will be listed in.

Tips:

To quickly assign a category without opening the Assign a Category screen you can:

• Start typing a category name and then select the category.

To quickly unassign a category without opening the Assign a Category screen you can:

• Double-click on a category in the Category box.
  OR
• Click on a category in the Category box, and then click the minus (-) button.

To order the category

When you exit from assigning the category the new categories are listed at the bottom of the screen. 

• This will now contain a list of each category you have added, and an order.  By default, articles are placed at the end of the category.
• Click on the order drop-down list beneath the category you wish to re-order
  
• Select a new position from the list
• Click OK to save the changes,