Spanish cedar (Cedrela, often Cedrela odorata) is not a true cedar. It is a tropical hardwood in the mahogany family. The cigar trade adopted it because it absorbs and releases moisture and has the familiar smell of a cigar box. Most wooden humidors and many cigar boxes are lined with it or made from it.
The wood has to be seasoned before you store cigars in it, because dry cedar draws moisture out of the leaf. See seasoning a humidor. It also adds its own aroma. Many people like this, but it is also why some collectors use other linings for long-term aging.
The empty branded boxes in the shop are often made of Spanish cedar. They are collectible woodwork, not a licensed tobacco product. Longer guide: Spanish cedar: why it matters.