If you want Roon to be able to access your music library that's stored on your Windows device, you need to first ensure that the folder is properly shared. Once the folder is shared it can be added as a watched folder in Roon. Please see the instructions below to properly share your folder:
1. Navigate to the folder where the media is stored via File Explorer
2. Right-click and choose Properties
3. Select the Sharing tab
4. Click Share
5. Make sure the permissions are properly set for read and write for the user then click share
6. You should now see the correct path on the Sharing tab
Once the folder is appropriately shared, you can enter the path, username, password, and (if necessary) workgroup into Roon in Settings > Storage. You can read more about this process
here.