From In-Portal User Manual

This tab manages the categories of the link. The list shows all categories to which this link belongs. The administrator can add and remove additional categories on this list. At least one category must be there, and exactly one category must be designated as the primary. The primary category determines the permissions for the link. To designate the primary category of the link, select the category and click on the Primary Category icon in the toolbar. The ‘primary' marker will move from the previous Primary Category to the one you have selected. </p>

The link will appear in all of the categories it belongs to, in the Administrative Console as well as on the front-end.