What are hives really? how does the body make them go away or shrink away?

Leaky vessels: Hives are caused by the activation of cells that release histamine and other inflammatory mediators that cause fluid to leak into surrounding tissue. These inflammatory mediators will be broken down by your body and will dissipate. Your body also makes Epinephrine (adrenaline) that can help stop the leakage.

Hives: More rarely they can be a part of hereditary respose involving the complement system and do not itch generally in that case.