All skills as have certain threat level they generate towards mobs. This means that when you cast a skill, it will raise your threat level and cause mobs to attack you and potentially ignore other near by attacking players.
Every skill has a aggro value (threat value). When you use a skill, this aggro value is added into a table in the game and this table is used to determine your threat level. Who ever in your group has the highest threat will become the primary focus of the mobs in that area.
Provoke and Taunt are the highest aggro/threat producing skills. As long as Paladins or Warriors keep these skills in cooldown, other players can attack the aggro'ed mobs without drawing attention to themselves.
Most maxed level skills only have a Threat Value of 5-10 per use. The table below lists the top Threat Valued skills in each class.
Threat levels for some skills:
|Warrior||Howl of Dread||34|