Triggered abilities use the word "when," "whenever," or "at." They're often written as "[Trigger condition], [effect]." Some keyword abilities, such as prowess, are triggered abilities and will have "when," "whenever," or "at" in their reminder text.

If the exiled card has an {X} in its mana cost, the value of X is 0 when determining that card's mana value.

Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities, like equip, are activated abilities and they have colons in their reminder text.