Wooden or Steel: Wooden and steel shields offer the same basic protection, though they respond differently to spells and effects.
Shield Bash Attacks: You can bash an opponent with a heavy shield. See “shield, heavy” on Table: Weapons for the damage dealt by a shield bash. Used this way, a heavy shield is a martial bludgeoning weapon. For the purpose of penalties on attack rolls, treat a heavy shield as a one-handed weapon. If you use your shield as a weapon, you lose its Armor Class bonus until your next turn. An enhancement bonus on a shield does not improve the effectiveness of a shield bash made with it, but the shield can be made into a magic weapon in its own right.
Source: Core Rulebook