Confused About yum

I am very confused about the operation of the yum utility on FC4.

Yesterday it performed an amazing thing for me. I typed

>yum install octave-forge

and it then proceeded to process 100's of packages and some 65 MB of
downloads. It successfully installed octave (a notoriously difficult
application to install) in one simple step!

But... I don't understand what's going on:

1. What is the meaning of the "octave-forge" string? Is this some
master RPM somewhere? Where? Is it an internet site? If so, how does
one locate such sites?

2. The man page for yum lists the functions "list", and "info,"
stating that they provide information on "available packages."
Available packages from where? All around the world? Just at
the FC extras site? The available packages on your system?

I could go on, but the answers to these questions would help get
me going in the right direction.
--
% Randy Yates % "Though you ride on the wheels of tomorrow,
%% Fuquay-Varina, NC % you still wander the fields of your
%%% 919-577-9882 % sorrow."
%%%% <yates@xxxxxxxx> % '21st Century Man', *Time*, ELO
http://home.earthlink.net/~yatescr
.