Panels and software
OS images
Ready systems the provider installs on a VPS when ordering: Ubuntu, Debian, AlmaLinux, Windows.
When ordering a VPS you pick a system from a list — the server is ready in a couple of minutes. Ubuntu and Debian are the most common: they have the most guides.
Some providers let you upload your own ISO or preinstall software — a control panel, Docker, 1C-Bitrix.