Tital says it all.

You don't.

You disenchant magical items you find in the world to learn how to apply their enchantments. If I found a Plate Boots of Sneaking (as unlikely as that may seem), then if I disenchanted them I would lose the boots, but I would learn the "+Sneak skill" enchantment which I could place on other items.

To place an enchantment on an item, you have to consume a soul from a soulshard. The better the soul, the better the enchantment.