To expand a little on what USAFRet said.
A server is a computer system that is made to be more resilient than a regular workstation and optimized to provide network services.
Spend time focusing on the software in a server instead of the hardware. The hardware is inherently more expensive, varying due to vendor differences, and hardware differences.
You can install Server 2012r2 on almost any modern workstation and begin to learn on that.
If you are curious about hardware, Dell & HP are popular vendors in the US, Fujitsu is popular in Asia for server hardware. For SAN's, EqualLogic, 3PAR, and EMC (I am forgetting many others here) are the old guard. For Network, focus on Cisco, Brocade, and Juniper.
For Software: Virtulization, focus on ESXi (vmware) and Hyper-V (Microsoft). Server: focus on Linux (Ubuntu, Redhat, Cent) and Microsoft Server 2012r2.
Are you lost on hardware yet? What usually happens in IT environments is that you inherit a bunch of crap that someone else purchased and you are stuck trying to support then replace. The software is much more important to learn than the hardware is.
Sorry if I rambled a bit here.