Good Stuff; for your future reference:
These are repository files that point yum to fedora repositories. Basically you can put any repo file in /etc/yum.repos.d/ and this will work.
You can think of your hosts file as being an internal DNS where you can add hostnames and IP's that your machine can thus resolve locally.
This is where you point your machine to external DNS servers for hostname resolution.
This is your yum configuration file where you set parameters that control the behaviour of yum.
Glad you've solved your problem!