377. Activated Abilities are repeatable effects with a cost. They follow a process of going onto the chain and resolving, similar to Playing a Card. See rule 349. Playing Cards for more information.
377.1. Activated Abilities are recognized by the presence of a ":" in the text of the card, preceded by a cost and succeeded by an effect. Example: "[2]: Draw 1" is an activated ability. The cost is 2 energy. The effect is to draw 1 card.