A storage cell is a physical location in your warehouse that remnants are assigned to. A cell has a name and X×Y×Z dimensions.
In the "Storage cells" tab you can create a new cell, see what is stored in it, and delete an empty cell (a cell with remnants cannot be deleted — move or write off its remnants first).
Editing and adding are available after paying for the production cabinet. Until then the section is read-only, with a large notice at the top.