NOTE THAT ONLY MACS CONNECTED VIA ETHERNET CABLE CAN BE WOKEN UP. There is no way to wake up any other computer using wireless networks. Also, only sleeping Macs can be woken up, not switched off ones.
To enable WakeOnLan on a Mac, launch “System Preferences”, select “Energy Saver”, then “Options”. Enable “Wake for Ethernet network administrator access”.
Note that you need to tell WakeUp the Mac’s “Ethernet ID” (also called “MAC Address”) in order to enable WakeOnLan. WakeUp will auto-discover this address when you use its “Scan” feature. Else, get the address in “System Preferences”, “Network”, “Advanced”, “Ethernet”, then “Ethernet ID”.