As Wikipedia says: “Windows Server 2016 is a server operating system developed by Microsoft as part of the Windows NT family of operating systems, developed concurrently with Windows 10”. The previous version was Windows Server 2012 R2.
It is available as a 180-day evaluation. You can download an evaluation copy of Windows Server 2016 for free. Go to technet.microsoft.com and click on the Downloads link at the top.
If you are setting up a local area network for the first time in an organization, you would first install Windows Server and then probably create a Domain Controller. Next you might set up a DHCP (Dynamic Host Configuration Protocol) server on your Windows Server. The next thing you might look at is DNS (Domain Name System). Before diving into any of these roles you will need to know a little bit about TCP/IP, networking in general and what a Windows domain is.