Ensure that your Dewalt miter saw is unplugged. If it is not, unplug it.
Remove the two screws holding the dummy cover in place, and pull the dummy cover off to expose the wire connections. You'll find the dummy cover located on the top of the handle.
You should connect the plugs from the work light's power box to the connectors accessed under the dummy cover, and replace the two screws to hold the light's power box in place.
Slide the plastic blade guard down to remove the four screws holding the black, plastic stopper in place. Remove the stopper, and plug the light assembly into the plug beneath the stopper. You can mount the light by replacing the four screws.