How do Clan Ladders work?
After you join a Clan, whenever you enroll in a Competitive Ladders that contains a Clan leaderboard, your result will be counted for your Clan as well. Your results will essentially count for both Ladders, your Solo one, and the Clans. If you leave a Clan and join a Clan after, your submitted results will stay with your old Clan, while your new developments will contribute to the new Clan.
How do Clan Ladders rewards work?
If a Clan scores high enough to win rewards, everyone in the Clan (both those who actively participated in the Ladder and those not) will be rewarded, including all players that were enrolled in a Ladder before leaving the Clan. Each member gets an even share of the total winnings, rounded up.