Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities (such as embalm from the Amonkhet set) are activated abilities and will have colons in their reminder text. Triggered abilities (starting with "when," "whenever," or "at") are unaffected by Ashes of the Abhorrent.
Ashes of the Abhorrent doesn't stop players from playing land cards from the graveyard if an effect allows them to do so.
If a creature dies at the same time that Ashes of the Abhorrent is destroyed, you'll gain 1 life.