I have a used GE Dishwasher. Do I hook it up to the hot water or cold water supply line?

As a rule all dish washers hook up to the hot water supply off the kitchen sink with a 3/8" supply. Shut the water off and remove the old hot water angle stop leaving the 1/2" nut and ferule on the hot water stubout. Replace the old stop with a 1/2" X 3/8" X 1/4" three way angle stop, (see image). You may now run the supply off the new angle stop. Don't forget to loop the discharge hose up as high as it will go in the cabinet and strap it in place or the tub will not hold water. Good luck, Tom