APPLE TV NOT WORKING

You do it using your computer iTunes.

iTunes menu > File > Homesharing > using the same Apple ID as the TV

FIrst, you don't need Home Sharing to use Apple TV. If you ATV is NOT WORKING, you should ask a more specific question. Second, to enable Home Sharing on your Mac, you need to fire up iTunes and select the items to share. Here is some info you may need Get help with Home Sharing - Apple Support. Especially check the firewall ports.