This data-source enables you to enter the folder path on the web-server's file system, using it to populate the items of a compatible editor, e.g. Data List.
The configuration of the File System data-source has the following options:
The first field is Folder path, here you can enter the local relative folder path.
e.g. https://leekelleher.com/umbraco/contentment/ or ~/umbraco/config/lang/
The next set of fields to enter Filename filter, e.g. *.css.
The value for the File System data-source item is a string.
Depending on the List editor used, this may be wrapped in a List<string>.