The Clan Store is available when you join a clan under the Clan tab. There you can buy useful items with loyalty points you get from clan tasks and from helping other clan members buildings and research. 

Most items in the clan store are also available in the in-game store where you can buy them with gold, although it is much appreciated to be able to buy them without gold but with loyalty points instead. Some of these items can also be found on invaders or by opening Loki's coffer.

Items are added to the Clan Store after clan chief or elders "procure" them from the Item Catelogue using a shared quantity of Prowess Points. Items can then be purchased in the Clan Store by all clansmen for Loyalty Points which are generated via clan tasks and clan helps.

Among the long list of items that can be sold on the clan store, most popular items include :

8-hour peace treaty : 20000 LP

12-hour increased offense : 2000 LP

12-hour increased defense : 2000 LP

50% increased resource production (7 days) : 15000 LP

Great greed (food, 7 days) : 5000 LP

15-minute boost : 2000 LP

60-minute boost : 6000 LP

3-hour boost : 15000 LP

Relocation : 35000 LP

Second Chance : 15000 LP

Clan task refresher : 10000 LP