Within the Gallery name area, insert a name for your gallery that will be used throughout the Fluid Infinity system of widgets, including your thumbnails and buttons. Your gallery name should not include any spaces and special or non-English characters. As you apply this name to other parts of the Fluid Infinity widgets be sure that it is inserted exactly as it is seen in the Container widget.
Source
The Fluid Infinity widget allows for you to select one of two ways to ultimately feed your gallery images. Select either Google Sheets or Thumbnails to instruct your Container where to pull your images from.
Google Sheets
Use Google Sheets to create a gallery that can be altered right from your Google account without ever opening Muse. With your Google Sheets key, you can add, subtract or alter each gallery items description, image and filter easily. The Google Sheets option allows for only container grid galleries.
For more information on using Google Sheets to load images into your gallery, click here.
Thumbnails in Muse
Use Thumbnails to load images through a selection of widgets found on your Muse page. With this option load images into your container grid gallery in bulk or individually or create galleries connected to single stand-alone thumbnails.
For more information on using Thumbnails to load images to your gallery, click here.