The storage system was added in the 13.0.0 update. It allows the clan to look at their fort and Siege items. The storage GUI shows the Clan Items the player has, and the parts they have, ordered by the rarity. If they click on the icon, it shows a description. It also shows the clan items they do not have. This system is in place so that players and clan officers/leaders can view the clan parts easier. It can only be viewed by people who are in the clan.