To make an accurate thermometer, we will need a slight modification. The other end of the thermocouple wires, where the meter leads are attached, need to be kept at the same temperature as one another. This is usually done (in a small laboratory like ours) by immersing those ends in ice water. Water with ice in it will stay the same temperature until all the ice has melted. You will probably want to insulate the wires where they sit in the water.
For our purposes, however, the far ends of our thermocouple wires are close enough to the same temperature that we can just leave them as they are. If they are one or two degrees different, that will affect the accuracy by one or two degrees, but we aren't using a meter that can notice that small a difference, so it won't matter.
Each different metal has its own Seebeck coefficient. That means that when it is coupled with a platinum wire (used as a reference wire in the table below) it will generate a certain voltage