My MTD mower blades will -engage I found a large spring small metal piece beneath the mower looks like a hook type piece of metal that goes somewhere but I have no Idea?

That is most likely the tension spring for the mower belt. Which exact model do you have? You can try to figure this out by pulling the spring to stretch it and then move the hook around to see if there is an attachment point or small hole for the hook. You can also try to buy a manual for it http://www.mtdparts.com/webapp/wcs/s...-_-mtd%20parts