When an app is selected in the Apps Panel, the selections relevant to that app are displayed in the selection panel. Selections may be controls, individual items such as animations, or groups of items.
For example, when the Animations app is selected in the Apps Panel, several groups of animations are shown in the Selection Panel. Selecting the Cats group then brings you down into the group of cat animations.
Cats group selected under the Animations app.
Cats sub-menu of Selection Panel.
The buttons at the top right of the selection panel are the Assign Hotkeys, Add to Playlist, Toggle All, and Hide Effects buttons: