Find the make/model of your NAS and either use its netbios name, or it’s IP address, which you ideally need to reserve/set ‘static’ either within in the NAS software, or via your routers DHCP reservation table using the MAC address of the storage device.

Note: - most common NAS devices may have a YouTube video to help you to locate its netbios name. So as an example the path might be (just as a simple example) //MyNas/ or you can use its IP address instead //192.168.0.116/ 

Then you need to add the ‘shared’ music folder path that contains your music library so that could be something like ‘/Music/My Music/ 

That ‘example’ means you would then add the shared library to Sonos, by adding either this complete path…

• //192.168.0.116/Music/MyMusic/ 
  or
• //MyNas/Music/MyMusic/

Every NAS is different of course and so your manufacturer support desk, user manual, or a YouTube video (perhaps), should help you to define the netbios share. In some instances the library share can also be protected with security credentials (username & password), so if that applies, then you need to make a note of those credentials too for use with the Sonos App. 

I guess the easiest way to discover your NAS IP address (if required) is via information likely found on your router configuration pages, where you may find details of all the products connected to the local LAN subnet.

To then actually add the NAS library path to Sonos and setup the share is fairly easy too and that is described in detail in this Sonos Support Page Link:

https://support.sonos.com/s/article/78

Hope that assists.

If you are using a MyCloud NAS, place your music in the “public” share.