The wiring in my kitchen only has two wires a black and a white. I have to connect or pigtail a piece of wire to the existing wires because the existing wires are to short to connect to the new fixture. When I connect the wires what do I connect the ground wire to? I understand match black to black and white to white:confused:

If the outlet box is metal, you can attach the ground wire to that with a machine thread screw. Keep in mind, even if the box is metal, it may not be grounded. If you test with a voltage tester between the black and the box and see 120 volts, then it is grounded, if not then no ground is available, just wrap the ground wire in the box and be done with it.