The instructions here worked OK for me. Perhaps you could describe what you have been able to do. Can you ‘see’ the share from the ATV menu? If so then the problem may be the authentication step.
The easiest thing to do is make the specific folder you need the share. e.g. if you have a drive on your mac /Volumes/MyDrive and it has folders /Movies, /TV make 2 shares: Movies and TV
Give the ATV the credentials to login in as a user who should be able to access the folders if they were using your Mac.