How do you connect four wire 240 volt to three wire device?

First of all,be very carefull.Hire someone if you can afford to.( I never did).Trust what noboby tells you about wire colors and where to place them on the device.Buy a cheap volt-ohm meter. You will use it in the future- great envestment! - $15 bucks. 240 volts (household), will be two "hots", one neutal and a ground(probably bare). read the device it will say LINE and LINE for the hot wires and neutral for neutral. It should have a green screw on it for your bare ground. Read about the use of your meter. You will think that you are Tom Edison before your next project. Good luck and be safe........Jim.