There are two wires to your light from the wall. one you leave intact. the other you cut a few inches from the light. That leaves you with 2 lose ends of wire. On your thermostat you should have screw terminals. You put one lose end of wire under each terminal. Then you mount the light in the incubator with the thermostat about 1 to 2 inches away with the flat side of the thermostat pointed at the bulb. Ad a fan if you have one on the other side of the incubator an plug it all up. It will take a long time to stabilize. You want to to watch the temp it kicks the light back on at. It should be about 99 degrees. Dont worry about the high timp till you have this. Once you have that then you can move the thermostat closer to the bulb till it starts kicking off before the incubator goes above something like 101.
Remember the thermostat only controls when the light comes back on. How close the thermostat is to the bulb controls when it turns back off. You may have to let it run all day befor you can adjust it.