The site machsupport is the Height Control Torch plugin by Brian Barker, but no description of how to work with it. Help me how to configure it and work with it?

That one, was written for a PLC controlled THC, with the Z being driven by mach in response to it, but you could use other devices....

It looks at the "Analog" voltage at the torch, that is converted by the PLC (or other device), to a integer value not to exceed 16 bits of resolution.
that value is then sent across a serial Modbus (using the old original modbus), and that is brought into the plugin as the voltage of the THC arc at present.
There is a PID loop in the plugin, that looks at that, and then adjust the "Z axis" to correct for THC up/down position.

So, in essence you will need:

a way to read the voltage at the arc, and get that into the old serial modbus.
you will need to pick a Torch XML, and set up your Z axis for toruch height control to be step/dir driven.
you will need to play with the PID settings on the PID config dialog.

Scott