The "Warehouses" tab in the "Stores" section is only displayed if work with warehouses is enabled in the "Warehouse" section.
This setting is useful if auto-reservation of products is enabled. Read more in the related article.
The setting "All warehouses are available" has two options: "Yes" and "No". If you select "Yes", then all warehouses added to the system will be available when autoreservation is enabled. If you select "No", then only those warehouses marked with a tick in the list below will be available.