Not a windows expert - but from what i've seen that means basically that there's no GUI.

https://en.wikipedia.org/wiki/Server_Core

Server Core is a minimalistic Microsoft Windows Server installation option, debuted in Windows Server 2008. Server Core provides a server environment with functionality scaled back to core server features, and because of limited features, it has reduced servicing and management requirements, attack surface, disk and memory usage. ... Most notably, no Windows Explorer shell is installed.^[1] All configuration and maintenance is done entirely through command-line interface windows, or by connecting to the machine remotely using Microsoft Management Console (MMC), remote server administration tools, and PowerShell.

Thanks Buddy. I think that answers my question.

With Server Core, there is no PerfMon.exe, Services.msc or Event Viewer available since these are GUI-based. You are administering the server through PowerShell commands (or "commandlets" as MS puts it). For example, to search an event log, you use a command like wevtutil qe /f:textstring <log name>. Similarly, you partition drives, configure the server to use a proxy server and install updates using commands.