Unless otherwise specified shields are composed of a couple centimetres thick wood and covered with hide, usually with a reinforced rim (often leather) and a metal boss.
Using a Shield
Raise/Lower - A generalised move for larger shields often done because you can't see past them and are just guessing where the next strike will land
Block - A more accurate use of meeting the incoming strike
Parry - A more skilled use, where you deflect the incoming strike
Bash - A shield is a large blunt weapon, why not prove it?