1. The FrontPage Server Extensions are a series of executables that were
designed to build certain types of web pages quickly. It dates way back,
more than 10 years, to when all we really had to work with was CGI and Perl.
Most users who wanted to get into web site design found Perl script
configuration daunting so the FP Server Extensions give FP a way to perform
some basic form handling operations without the user having to setup scripts
and such. The FP Server Extensions also enable publishing over http. This
let's an application that can make use of the extensions communicate
directly with a web server, instead of simply transferring files onto the
server via FTP. The FP Server Extensions are used by Visual Studio to
transfer files over http to a web server running the FP Server Extensions.
You don't really need to know anything about the extensions as there isn't
anything for you to do with them (other than publish via Visual Studio) if
you aren't also using FrontPage.

2. IIS has three main services built into it:
       Web publishing services - to serve web pages
       FTP services - for creating FTP sites and responding to FTP requests
       SMTP services - for transfering mail through the SMTP protocol
(useful if you need to send emails outbound from an application and want
control over the outgoing server)

There are all sorts of things you can learn about IIS. How to write scripts
that can be run on the server to perform certain management tasks (creating
web server instance, new virtual directories, etc.), how to keep it healthy,
how to secure it properly. It all really depends though upon what you're
looking at. If you're looking at it as a developer, then you will need to
know how to configure it and work with it at a basic level at least. This
will help you out when you're building web applications because you may find
what works on your test server doesn't work on your production server
because you need to take some IIS setting into account. If you're looking at
it as managing production web servers then you definitely want to look much
harder at the internals, how it works, and how to keep it from breaking.