Well, it *can* be instantiated, but not by the constructor
that you can't call. There are a bunch of static "factory"
methods that return InetAddress instances; that's how you can
get hold of one.
It's true that "factory" methods don't stand out in the
Javadoc the way constructors do, and this can make them a bit
difficult to find. Eventually, though, you learn to look
for them ...
Answer #1: Sometimes there is, sometimes there isn't.
Answer #2: Javadoc is intended as a reference where someone
can check the fiddly details of something partly understood
already, not as a teaching tool or introduction to a topic.
Answer #3: Javadoc is written by programmers, and some
programmers write Java better than they write English. ;-)
Sun's on-line tutorial
is a reasonable place to start. Among other things, it has
a chapter on networking (but I haven't read it and can't vouch
for its ability to teach). Give it a whirl.