If you get a server of your own, it will operate independently, so it will have its own Operating System and you can later install server side programs directly or script-driven internet sites through a hosting Control Panel. While keeping the Os updated isn't always considered an absolute necessity, it can be a really important task for several reasons. A more modern OS version could have better support for certain hardware, so you could get better performance for the sites and web applications that you install. Your server shall also be more safe because updates typically include security patches which take care of small issues that may enable unauthorized people to access your content. Last, but not least, newer script versions, which are also released for both increased security and for additional features, might require a later version of the Operating System in order to work correctly and with their 100 % capabilities.