The fields in the "Add new network drive" part of "Network drives" section should be self-explanatory, but there is some ambiguity in their use especially for users not familiar with how Linux handles SMB.

"Browse network" button: although this is the simplest way to get fields pre-filled, it is not guaranteed to work on your network or with your NAS or Windows share folder. If nothing shows, just fill out the following fields yourself.
"Server" field: here you enter your PC/NAS hostname or IP address - without any prefix (like 'smb:' or '\\') or suffix (like '\' or '/').
"Path" field: enter just your sharename (like 'NASMusic'). If you want to share a specific folder append folder name (like 'NASMusic/DSD64') or longer folder path (like 'NASMusic/DSD64/Jazz'). Again, there is no need to add any '/' or '\' before or after the path.

After you click the "Add network drive" button the "Enter credentials" dialog appears. Keep in mind that even if you have set up your share to have public access without authentication, you must set-up some username or password for Euphony to use your share.

After entering your credentials ("Domain" field is usually "WORKGROUP" or just leave it empty) click the "Add network drive" button. The system will try to connect to your share with the given options and report success or failure.
In case of failure the reported system message will probably be unhelpful but there are several main reasons for the failure result:

• Re-check the server hostname/IP and path fields and make sure to observe the above suggestions for these fields
• Re-check entered username and password
• Make sure that your username/password does not contain special characters like: , . ? * ` and the like - it is best to use only alphanumeric password
• In the "Enter credentials" dialog, try selecting a different SMB protocol version ("Ver." field)
  
• If you try out all "Ver." options without success, try different security protocols ("Sec." field)
• Make sure to try all combinations of Ver. and Sec. options until you succeed

(Note that the above suggestions are precisely ordered to minimize the number of attempts before a successful connection)

If you are sharing a folder on Windows OS it is possible that some security settings prevent successful connection. The best thing to do is to just enable SMBv1 protocol as it offers the least restrictive security. Then select "1.0" in "Ver." field in the "Enter credentials" dialog. Here is the link on enabling SMBv1 on Windows: https://docs.microsoft.com/en-us/windows-server/storage/file-server/troubleshoot/detect-enable-and-disable-smbv1-v2-v3

So far we have not had a case of Euphony not being able to connect to any SMB share or NAS but sometimes it may take you a while to succeed with a precise combination of options.

After a successful connection, your "Network drives" table will show a new row: it is uniquely identified by the "Name" field constructed as a combination of "Server" and "Path" fields. Your network drive is now connected: you can browse it in Files view of the main Euphony app or in a separate File Manager application. From there you can copy folders or files to your Euphony drive. If you want your whole added share to be part of the library choose "Add to library" option from the three-dot menu at the end of the network drive row.

Note the "Linked" column: this is the actual path where your drive is mounted. You may need to add it to Roon library if you use Roon core on Euphony.