Preparing to install macOS Server
If you’re going to install macOS 10.14.4 on an existing computer and want a clean installation rather than an upgrade, use Disk Utility to erase the storage your volume is on.
You can use Disk Utility when you begin installing. For instructions, search Mac Help for “Erase and reinstall macOS.”
Volumes on partitioned storage
Partitioning storage creates a volume for macOS. The volume you install macOS on should be at least 10 GB. This volume should be larger if you plan to store additional data on it.
The volumes on partitioned storage are often simply called disks. Each volume appears as a disk in the Finder, and you use each volume as if it were a separate disk.