Follow the circuit diagram above to reference the wires are connected. You will need to solder wires to the Trellis PCB and 4 potentiometers. Use male jumper on the Trellis wires to easily connect to the headers on the Leonardo.
The Trellis PCB will have 4 wires, SDA, SCL, GND and 5V that will connect the SDA, SCL, GND and 5V pins on the Arduino Leonardo.
The 4 pots have common ground and 5V power in series. The middle terminals connect the the A0-A3 pins on the Arduino Leonardo.