Before you do anything else, go to the Unofficial Fedora FAQ
and read what they have to say about yum. Then move on to Stanton Finley
and read his yum section. If you still have questions after that go ahead and ask
An alternative way of getting the repos is to install yumex
which will install a number of repos automatically and give you a gui interface to enable/disable repos install/update/uninstall apps and get info an all avialable apps + agreat search function.