Ubuntu is a free, open-source Linux distribution based on Debian.
Canonical - its main sponsor - releases three editions: Desktop, Server, and Core (for IoT devices and robots).
The LTS version ships every two years in April. Interim releases ship every six months between LTS versions.
LTS gets security updates and free maintenance for five years; the interim version gets nine months.
Canonical names Ubuntu by release year and month.
Ubuntu 20.04 LTS "Focal Fossa" shipped in April 2020, supported until April 2025. The next LTS is Ubuntu 22.04, supported until April 2027. Between them are Ubuntu 20.10, 21.04, and 21.10; 21.10 is supported until July 2022 (nine months).
Download the LTS version from ubuntu.com.
Burn jammy-desktop-amd64.iso to DVD or USB, and set the BIOS to boot from it. I usually burn to USB with https://www.balena.io/etcer/.
Etcher runs on Linux, macOS, and Windows:
Search Google for "boot from USB" + brand. Example: "boot from USB Dell", "boot from USB Lenovo".
Install: select Ubuntu at GNU GRUB, wait; choose English, click "Install Ubuntu"; Keyboard Layout, "Continue"; "Normal installation"; read "Installation Type" options and choose; timezone; mandatory fields, "Continue"; wait for the copy; restart; unplug USB, press Enter.