Arms Warriors are battlefield tacticians who focus their rage, waiting for the opportune moment to strike their opponents with overwhelming force. They are heavily armored destroyers who specialize in dealing precise strikes, skillfully parrying incoming attacks, and regenerating their health anytime the enemy fails to attack them, all the while deftly maneuvering around the battlefield. The Arms Warriors defining ability is Colossus Smash.
An extremely useful tool for overall optimization
WoWhead Arms guide
http://www.wowhead.com/arms-warrior-guide
Icy Veins Arms guide
https://www.icy-veins.com/wow/arms-warrior-pve-dps-guide
Noxxic Arms guide