Normally,with the exception of something like the sneak preview recently for Over There,,it will record the showcases nightly automaticly with no intervention or setup.(New ones do not necessarily occure every night) However,you need to make sure those channels are set in your "channels you receive" settings. If they are not,it will not catch them.
Also in regards to NFL highlight showcases,I found out last season that those are not automatic to everyone. I had erased all my suggestions,and after that I did not get Highlights again until after I recorded another game,and the system saw it as a preference. (did not have NFL ticket). Chances are, just giving any NFL game a "thumbs up", without actually recording will probably do the same thing.