The files you list above normally live in /etc/yum.repos.d/
This directory is referenced by the yum.conf file which also lives in the /etc/
The files contain information pertaining to channels (repos) which contain xml indexes of rpm files.
The fedora repo files actually point to mirror lists rather than to actual repo servers but the mirror lists do point to the repo servers.
If you edit a file in your favourite text editor you will see something like this (fedora.repo):
name=Fedora $releasever - $basearch
[fedora] - the name of the repo, how it is addressed in yum name=Fedora $releasever - $basearch
$releasever and $basearch are variables which convert to your release and basearch automatically so fc8 and x86_64 for example.
The baseurl points directly to a repo location. The mirrorlists well guess what they point to mirror lists which are just a list or mirror servers.
Enabled=1 means that the repo is enabled. 0 would mean not enabled.
gpgcheck=1 tell yum to check that the rpm downloaded has a key and that it matches the key located in the gpgkey file.
In 99% of the time setting up yum is simply as case of rpm -Uvh or rpm -ivh yum.rpm
Likewise the repos normally come in rpm format so it is just a case of installing them using rpm or yum.
may help you?
Fedora has new repo files now with the words newkey in their titles worth getting them as they have a new signing key for the rpms.