I would suggest to search for the documentation how to handle files and pictures in Mendix. If you have unterstand this logic and how to handle with the generalization of the system objects, you will unerstand to use this widget.
If you have any specific problem, feel free to ask. It is helpful to see you datamodel to understand the specific question.
as Gerrit pointed out, have a look at the documentation:
For downloading multiple files, take a look at: