Image creation
Any device running Ubuntu Core is instantiated from an image. This image contains little more than the kernel, an init process, and a few essential tools. On all but the earliest releases of Ubuntu Core, even the snapd daemon that manages snaps is itself installed via its own snap.
Pre-built images are available for supported platforms, including Raspberry Pi, Intel NUCs and x86/KVM virtualisation, and these can be download and easily installed. See Supported platforms for the current list and for download links to both the images and the model assertions they use.