As part of the Unified Community Platform project, your wiki will be migrated to the new platform in the next few weeks. Read more here.
Each card can have one usable ability and some types of card have a passive ability. When receiving or buying a card, that card is assigned an ability. Meaning you can have 4 peasants with 4 different abilites, which one you choose to bring with you into a game will may determine the outcome.
In a later patch you will be able to aquire skillbooks which you can use to change your creature ability.