Once the Video Showcase add-on is installed, you will be able to see it in the Templates for your galleries. The showcase features one large video on top of the thumbnails that changes whenever the thumbnails are clicked.
For each gallery you can create a description that discusses your gallery or adds extra information for anyone viewing the gallery. If enabled, you can choose to put the description above or below your gallery (default is above).
From here you can also reset all of the gallery options to the defaults by checking the Reset option. The action cannot be undone and you will lose any previously saved options for that gallery.