To work with Storages, click the button in the Main Toolbar or select the menu item "File > Inventory > Storages", or use [Ctrl+4] keyboard shortcut.
Storages tab allows you to define your storages where your material is kept. Storage numbered 1 is pre-defined storage (Default) and it is not possible to delete it. You can change its Description for better customizing. If you don't define other storage when defining plan, pre-defined storage (Default) will be used.
Sources tab allows you to see the list of materials stored at currently set storage. It is not possible to make any changes in this view; it is for information purpose only.