An Ability is a basic attack, special attack, or an action to heal or buff allies. While Basic attacks can be used as often as you want Special attacks need to be charged with energy to be ready to use. After once used they need to recharge. A number on the Special attack Icon displays the number of turns that Hero has to wait before the Special can be used again. The Chilled debuff prevents the gain of energy. Some "attacks" have different effects when used on allies or enemies like Ember Sanguine first Special Attack or Bauble's Basic attack.
Each Ascension of the Hero unlocks (adds) a Special attack.
Basic attacks do not rely on energy and can trigger Epic effects. In comparision to Special attacks they do much less damage.
Traits are passive abilities and shown on the Hero's profile. Tap and hold the icons to get more info about them. Traits often affect team allies or enemies in an encounter.