The Basic Information pane appears at the bottom of the sidebar, and displays a brief summary of the photos you've selected. If no photos are selected, it displays a summary of the entire collection. You can toggle the display of this pane using the View ▸ Basic Information command.
The floating Extended Information window displays more information about the selected photo. The View ▸ Extended Information command or Ctrl+Shift+X toggles the display of this window.