I have a Carrier furnace and want to wire the humidistat directly to the furnace. Where does the white wire go and do I need two or four wires for the himidistat

The Two wires from the humidistat will connect to the "C" and "W" terminals on the furnace . Some furnaces have designated terminals for the humidifier, if connecting to the "W" from an older mechanical thermostat you may have to adjust the heat anticipator in the thermostat, it is also common to wire the humidifier using a sail switch so that when the fan is in operation the humidifier will operate through the humidistat.
Good luck, Mike