Talents are unique selectable abilities that warriors and rogues can use. Mages do not use talents and have access to spells instead. The Wardens receive one free talent based on their origin, two at character generation and one talent per level. Talents have special animations that distinguish them from standard attacks.
The character executes a special attack or action (e.g. bashing your shield into the opponent, sending them flying).
A permanent bonus, change in game mechanics, or upgrade to an existing ability (e.g. adding a chance of stun to all two-handed attacks).
While activated, the Warden character gains some bonuses or some game mechanics will change (e.g. using your shield to increase your cover vs. missiles).
Important note for power playing: activating a sustained ability will only cost mana/stamina if the mana pool is full. Knowing this allows you to use mana first, and then 'reserve' the empty bit of mana pool for sustained abilities. see tactics to take full advantage of this.
Note: It is possible to stack some sustained talents as long as there is at least 1 remaining point in the stamina pool. But if the player uses all the points or an attack drains all the stamina, then the talents are deactivated and you have to wait until they cool down before you can use them again.
Many talents should generate threat on hit/activation. In addition to the threat number found in talent mechanics description (multiply by 10 to get the actual threat value), any damage dealt by the talent should generate additional threat. This additional threat is based on the damage amount in relation to an enemy's maximum health. E. g., dealing 50 damage to an enemy with 100 hit points should generate 50 points of threat -- in other words, the formula is 100 * (damage/enemy health at fully healed hitpoints). However, as of patch 1.02, no activated talent, except Taunt (with or without Frightening Appearance passive bonus) and Threaten, will generate any additional threat. The root of the problem is the AI_Threat_UpdateAbilityImpact() function, that gets properly invoked for spells, but not for talents. The additional threat info is left intact in the specific talent mechanics descriptions: hopefully, the issue will be resolved in Dragon Age: Origins - Awakening.