Labels can be added to Tickets from the header in the content panel:

To add a label click  Add and the labels that exist in your helpdesk will appear in a dropdown menu, or you can enter a new label.

If a label has been applied to a Ticket, you can see it in the labels section of the navigation panel:

On the Navigation Panel, labels are displayed in alphabetical order.

Click on the label to load up all tickets that have that label added in the view panel.

You can also load a list of tickets with a label added to them by clicking on the label on an open ticket.