When it's talking about the adding of "?show=P" and whatnot, there's an 'and' that should be an 'or'...
"You can use custom friends groups, which are described at http://www.livejournal.com/support/faqbrowse.bml?faqid=102, or you can append ?show=C
Meaning, they want to append one of those things to their URL, not both...