Do you know what version of Windows server you are planning to fiddle with? 2003 and 2007 are nice enough, there were some pretty crazy good additions to 2012 though on the interface and scripting fronts. The basics still hold and hopefully there will not try to trip you up with concepts like primary domain controller and backup domain controller (once very important, made pointless by newer versions of server).
Active directory and the concept of domains (as in local network) then. I would take it all the way up to Organizational units (a way to segment networks, usually between divisions).
Straight active directory is good. For the most part it is cut above standard network shares (really fine grain controls over what a given user can do) and the option to have user names and passwords set and changed centrally, there is more to it but that is pretty much it. You will probably not have played with it before as that is most of what the pro/business/ultimate lines of whatever windows you are on do above the home stuff. There are many ways to join a domain but where you change your computer name/workgroup is where you can join in the appropriate versions of windows.
WSUS is probably worth knowing of -- if you have 20 machines and there are 50 megs of updates on a given patch Tuesday you do not need 20 machines nailing your bandwidth, and you certainly do not want to be wandering around and pressing update on 50 machines. This allows you to store MS' updates on your server, it also allows you to more easily choose what updates get applied; it may be a trifling minor update but still good stuff, however if it breaks your accounting software because reasons* or some business critical program and nobody in the company can use it then guess which person gets yelled at?
Related to the above there is group policy objects aka GPOs. They have two main jobs in setting options/restrictions on a machine (remotely/at the server if needs be, see also RDP) and installing software remotely, however you will want a proper installer for this (see MSI) and a lot of our favourite programs do not have this -- firefox has a few people playing in that world but for the most part it is not great and that is another reason you still see internet explorer in enterprises (you might be able to do something with ninite pro).
http://support.microsoft.com/kb/816102 and
http://www.advancedinstaller.com/user-guide/tutorial-gpo.html has more.
The network will be running a local DNS server, as long as you know what a DNS server is and what DNS does it should be OK and you can go with
http://xkcd.com/627/ for the rest. Most will tend to use it as a far better alternative to network discovery.
*mention you will want a machine to trial this sort of stuff on. Even a virtual machine will do these days though if it can be a clone of the rest of the machines then push for it. Virtualisation is very big these days and sadly virtualbox is not quite the thing you will be playing with, that honour probably going to VMware (it looks much like virtualbox in the consumer one, big boy one is a bit different but that XKCD cheat sheet above holds true) though things like proxmox are good and in the very high end world you have citrix too.
If you can look as though you are not completely phased when setting up an exchange account for a client computer that is good. Exchange is pretty hot though so you mainly just have to type the server location and the username you want on it.
Backup and restore is big. Everybody uses something different here, say you know what clonezilla is though so at least you have something. Depending upon how old school there are they might refer to it as ghosting (as in Norton Ghost, one time backup program for everybody, nowadays very middling but not bad).
About the only other thing is windows server is typically where you see IIS, IIS is Microsoft's web server but it also speaks ASP.NET (basically C# but for web developers, it will take pointing a weapon at me for me to say it but it is very nice) and can speak to active directory to allow all sorts of fun web applications to be developed. Know what it is but if you are cramming the rest tonight then ignore it all. I guess there is also MS-SQL (Microsoft's take on SQL) but leave that alone.
I seem to recall you are the token IT person for your circle of friends and family, that is good because everything else is the same as that except you might be doing it over remote desktop. If you do not start crying when you are presented with a batch file then you are there. No doubt they could ask questions that see you running for the manuals, it sounds like they want to make sure you are not a complete liability though.
