Find the plug computer IP address (check your DHCP server), and launch the Amahi installer by visiting http://plug_computer_ip:2000
(Use nmap or ping -b to find new devices on your LAN, if you can't find your plug computer IP address on your DHCP server.)
It will ask for an install code. That code can be obtained by creating an Amahi profile here: https://www.amahi.org/user (you'll need to create an account first, if you don't already have one).