Custon Fields On – Off

I have a problem: S
I’m making a site that contains multiple threads, videos, news, photos of parties, among others …

and I’m putting in a news statement of partner sites, eg by: Site Name

I would like to do this using custom filds, know how to use the system,
only wanted some code that was more or less like this:

the lowrider fild is completed, display it.
if not, does not display anything.

I think it’s pretty much it. can anyone help me? , x

Portuguese into English by google:)