You’re used to only seeing one room in the house, the one which has your Desktop, Folders and Applications. (Read: How to partition a Mac hard drive or SSD, or create a APFS volume for more information.) Think of your hard drive as the house, and the volumes as different rooms. A hard drive is typically a single volume, but it is then split up into multiple areas, known as partitions or volumes. They just see the whole drive as one thing. Most people don’t really think about their hard drives (well, SSD these days) in terms of partitions.
