Uses Shield Wall if you are in Defensive Stance and have a shield equiped. If you are not in Defensive Stance it will switch you to Defensive and equip a one hander and shield of your choosing (Fill in the brackets with the name of your equipment.
#showtooltip Shield Wall
/cast [stance:2,equipped:shields] Shield Wall; [stance:1/3] Defensive Stance
/equip [YOUR 1H WEAPON]
/equip YOUR SHIELD