Based on XBMC / Kodi this is a customized Android media center software with which you can play music, videos, pictures. This works both with streams from the Internet, as well as with local files on a NAS eg Unfortunately, the connection of a USB disk or a USB flash drive does not work because the USB port of Fire TV does not allow. It even goes live TV via the Fire TV. The operation is possible via the included remote control of Fire TV.
Unfortunately, an installation on the Amazon App Store is not possible because the software is displayed as incompatible with the Fire TV, which is completely incomprehensible to me, because it works absolutely perfectly.