Artie and I have been touting the benefits of APFS and throwing around a lot of terms you may not understand. I wrote the following for a friend who's computer skills are similar to yours and thought it might help you understand what we are talking about.
Originally Posted By: joemikeb
Drives, Partitions, & Volumes
 for the Non-Technical
The term “Volume†has been around for a long time but is largely unknown to the non-technical users and a large percentage of “power usersâ€. The advent of Apple’s new APFS file system, which is required for Catalina (MacOS 10.15) has brought the term into new and important prominence. This in turn has lead to some confusion about the relationship between the physical drive, partitions on the drive, volumes.
Definitions:
Drive: The physical device used for data storage
Hard Drive (a.k.a. HD, Rotating Rust, Floppy): A drive that uses magnetic (iron oxide) on a rotating disk to store the data. There are lots of moving parts which slows data access significantly.
Solid State Drive (a.k.a. SSD, Thumb Drive, SD Card: a drive that stores data electronically and unlike an HD has no moving parts.
Partition: An allocation of the physical capacity of a drive. Partitions can be added to a drive non-destrucivey (without deleting or damaging data already on the drive) and in some cases partitions can be removed destroying only the data in the removed partition, but that is not always the case. (The Rule Of Thumb is “Never repartition a drive unless you have a known good backup of all the data on the drive you do not want to lose.â€)
Volume: A logical structure all the data is stored
Every drive has at least one partition and every partition has at least one volume.
APFS The Game Changer:
In Apple’s old file system, MacOS Extended (HFS+), a partition could have only one volume and that volume had the same capacity as the partition it was on. Not so with APFS. In APFS…
A new logical structure is added called a Container which can contain multiple Volumes such that Every drive has at least one partition and every partition has at least one Container and every Container has at least one volume.
Each volume can potentially occupy the full capacity of the partition
Volumes can grow or shrink depending on the need or can have a fixed maximum capacity if desired
Volumes can be created or deleted non-destructively
APFS is optimized for use on Solid State Drives, but it works on HDs with a slight performance penalty. In use…
APFS volumes are far easier to create and delete than partitions.
APFS volumes are far more flexible than partitions.
APFS is now Apple’s recommended solution.
There are currently unexploited features of APFS such as “Snapshots†with the potential to render backups obsolete.
Experience with APFS is proving it to be very stable and reliable.
The only reason for using HFS+ is Time Machine (Hard links that are used throughout Time Machine are not supported in APFS)
