You must complete challenges to gather points for your Clan. To get rewards you have to complete at least one Challenge.
As the Clan accumulates points, reward tiers are reached. Each reached tier means more rewards for everyone at the end of the event to choose from. Clan XP can be rewarded from each reached tier.
If there are for example 4 reward tiers and the Clan reaches tier number 3, everyone can choose 3 rewards for themselves at the end of the event. The Clan receives Clan XP from all tiers with Clan XP as a reward.
The reward tiers are not affected by the level or number of Clan members. All Clans have the same total points cap and tiers in the event. Now's the time to grow your Clan!