It is used as a separator / wedge. It goes between the top of your headlight and the fender, near the edge of the hood.
When you took the big cover off that sits above the rad and goes from the fender on one side to the fender on the other side, there were 4 small plastic pins you had to take out. The pin that goes into the fender, one on either side, is where this wedge goes, under the fender and on top of the headlight (between the fender and the headlight). The plastic pin for the rad cover is what will go thru the hole in the wedge, so just put it between the fender and headlight, line it up with the hole in the fender, put the rad cover on and put the plastic pin in and it'll keep the wedge in the right place. The "L" on it indicates its for the drivers side.