I'd begin by doing a search on the term
x-link if I were you.
That should tell you all you need to know. 👍
Failing that consult the FAQ section at the top of this board, titled "Look here
before you ask" which has a complete guide to setting up an online session.
But of course you've already done that haven't you?

As a general rule, always search first, try slightly different search second, (make sure you're searching the correct forum too, it's pointless, for example to search the GT3 forum for answers to GT4 questions,) and if you still can't find an answer, then start a new thread, otherwise the boards become terribly cluttered with people asking the same question over & over again. e.g. "Why can't I race in the Professional Hall GT World Championship?" which has been asked nearly a million times now!!!!
Hope that helps, welcome to GTP, enjoy your stay.
*edit* looks like I'm superfluous, Famine has beaten me to it!