You need an external 10v (12v will work) power supply.
I'm not familiar with your VFD, but I used the wiring digram in the link below.
http://www.homanndesigns.com/pdfs/EN010_V8.pdf
The red 10+ is the V+ from your power supply, connect this to 9 on the G540. The Blue Ground is the ground from your power supply, connect this to 7 on G540. Then connect the G540 pin 8 to your VFD Vout (or VFD command input). Then finally connect the power supply ground to the reference VFD ground. For my VFD I didn't need to supply V+ reference voltage to the VFD, it works fine without it, but your's might need that.
For turning the spindle on, use the solenoid in the diagram above and wire it up the same using an output on the G540.