With the power off put the ac voltmeter probes into a 240 VAC receptacle's two hot legs. Now turn the power on. If it is 240 link the welder for that voltage. If it is 208 link accordingly. The green or yellow with green stripe or green with yellow stripe is the earth ground to chassis of welding machine. The white and the black wires on the cord are usually wired as the two hot legs. Tape off the red if it is a four wire cord.
In the house wiring, for 200-240 VAC stoves & dryers the use of 4 wires is to provide a separate wire for neutral and a separate earth ground. This permits 120/240 by using a neutral, one hot and the earth ground for the 120 and all wires for 240. Welders do not require 4 wires for single phase.

I think perhaps you should give a friend with some more experience some beer to wire your welder up. There must be someone around in your world who would be willing to help you. The price of a dozen beer is VERY minimal compared to all the possible things that could happen if the welder is wired incorrectly or proper safety procedures are not followed during the job.
darren

Begging to disagree- in a 240V single phase circuit the two hot leads should be the black and the red, the white is neutral, the green is safety ground.  If the equipment being serviced contains 120V components (often cooling fans, indicator lights etc) the neutral wire may be necessary.
Bill