In the tag tree (left panel), navigate to and click on a desired tag to activate it.
Tagged items will be displayed in the right panel.
You will see the active tag in the Address bar, along with other related tags next to it (greyed out when not selected). Related tags are tags which have common items with currently activated tag(s).
Activating multiple tags
Click on another related tag to activate it. You will now see items that are tagged to both tags.
Alternatively, in the tag tree on the left pane, Ctrl + click (or middle mouse button click) on another tag to activate it.
