Ubuntu is a Linux distribution based on Debian GNU/Linux. There are Live CD versions which allow later installation and versions meant only for installations.
Download an ISO file from https://ubuntu.com/download and burn to CD or install to USB key with unetbootin, if you plan to install it on a server there are two installer versions Ubuntu Server and Ubuntu Server Live [1].
Ubuntu 18.04 LTS (BionicBeaver):
snap search canonical
, such as Docker, Kubernetes, microk8s, aws-kernel or azure-kernelUbuntu 16.04 LTS:
You can also visit wikipedia:Ubuntu_version_history or https://wiki.ubuntu.com/Releases for a detailed list of versions and changes
Canonical provides official support for Ubuntu