It is not a tool, it is a skewer and by the looks of it not a bike shop quality bike? It holds your front and or rear wheel on the fork in the front or in the drop outs on the rear. I suggest that you put as much of this bike together as you can yourself and then take it to a bike shop to have it checked since you do not know what a skewer is.... this could prove detrimental to your health if you do not! This is obviously the part that holds your front wheel on! Your rear wheel was obviously a bolt on wheel? if so take this bike back to wherever you got it and get your $ back now.