Both. For streaming from your local network, you need to have a DLNA (or also called UPnP) share server set up. Most NAS devices have such a server built in and only need to be activated. Every PC or MAC also has sharing possibilities. Whit e.g. Windows 10 as follows:
press the Windows button
Search for “Media Streaming Options” and click the result to open Control Panel on that section
Click the Turn on media streaming button to enable DLNA on Windows 10. Turn on media streaming on Windows 10.
Click OK to apply the settings and complete the task
It is easy: activate sharing on your PC or NAS, press the Media button on the TV PLUS remote control and wait a bit. All DLNA servers on your network will be automatically scanned and shown. You can also consult the Internet about DLNA, there are many articles covering that topic.
You can also play music, videos and photos from a USB stick. Just plug it into the box, press the Media button on the TV PLUS remote control and select the USB drive.