You strap a large or larger shield to your forearm and grip it with your hand. These exotic shields are so heavy that you can't use your shield hand for anything else while using one, nor can you make shield bash attacks. Wooden and steel shields offer the same basic protection, but they respond differently to special attacks (such as warp wood and heat metal). You need only take the Exotic Shield Proficiency (extreme shield) feat once to use both the wooden and steel versions proficiently.