The DEPOT tab allows you to maintaim a "depot" for each customer. A depot is a list of products and the number of each products that are available in the depot, eg. number of bottles of soap.
This has to be enabled in the Users module, in the Restrictions settings. You will be given a warning when you need to do inventory on a depot.
You have to fill in a few basic details about the depot:
Click on the Add product button to add a product to the depot: