Related reading here
. Autoten is like a script on steroids that installs all sorts of third-party stuff that the Fedora Project won't touch, like the stuff on the "Forbidden Items" page. It's trustable and lots of folks around here use it. Yes, Autoten will install Adobe Flash.
And a codec is, well, a codec. http://en.wikipedia.org/wiki/Codec
The most common codec people notice "lacking" from Fedora is mp3; Autoten can help you in that department too.