Cards are most often collected through chests which can be won from events, found during Raids, or purchased with coins. When it comes to finding new Cards, the village level determines the cards that can be found in chests and their rarity as well.
Another great way to collect cards is by trading with friends. Normal Cards can be traded at any time within the daily limit, and Gold Cards can be traded during special events.
Lastly, cards can also be collected in very special events and chests!