Managed servers comes with a basic setup. A basic setup includes updated OS installation, control panel installation. In other words, your server is maintained by the server provider. Server admin takes care of everything for you. While unmanaged servers are opposite to it. In an unmanaged server, you are responsible for everything. The server provider gives you a blank server without anything installed even an OS. Some provider offers just OS installed on unmanaged server. You have to install everything on your own. You must be a Linux expert if you are planning an unmanaged server. OR you can crawl user guides available on google for a server setup.