They are used towards progress of Adventurer's Challenges.
When earning challenge points you will see them on the in game screen along with fame and any silver or resources if the proper setting is enabled (key icon). Once a player has completed all challenges for daily, weekly and monthly they will no longer be earned until the next 21 hours. Completing daily only for example will still show more earned which contribute to weekly and/or monthly challenges.
Challenge Points are also included in Guild Challenge.
Way to Earn Challenge Points
|Action||Rewards Challenge Points?||Amount Rewarded|
|Farming (Animals)||Yes||Varies by Tier|
|Gathering||Yes||Varies by Tier|
|Defeat Mobs||Yes||Varies by Tier|