IF you have a Raspberry Pi 2B or 3B with any recent version of FPP installed.
The "easiest" and probably cheapest way I've found to use Relays for control of AC lights is to use the USB Relay boards sold by www.ICStation.com
They plug into a USB port on a RasPi. The 2 Relay and 4 Relay models get their operating power from the USB port. The 8 Relay board has a 5vdc power input.
Add them in the Channel Outputs "Other" section. Pick USBRelay, then ICStation, then TTYUSB0 to control. They work like a DMX device then (Universe and channel).