The cache is simply an inventory for your kinship that acts similar to a shop. Only ranking members, Game Masters, and KinshipKeepers have access to see and interact with this. This allows ranking members to buy or withdraw a private selection of items and funds.
Because the cache works very similar to the shops feature, we will skip the basics, but you can read more about them here: Campaign Shops.
Manage Container Permissions
The main difference between the cache and shops, is you can manage permissions per container. This allows you to give access to certain items only to specific ranking players.
To get started, create a few containers within your kinship cache, and then click the blue "Manage Container Permissions" button at the top.
On the Manage Cache Container Permissions screen, you will see each container with checkboxes for the rankings. Adjust as needed to control which ranks have permissions to View and Withdraw items inside.