Yesterday in a post I saw something indicating that if you try and
joint pieces larger than the width of your jointer you run into
problems with the grain direction. Can someone explain this to me? I
have a newly aquired jointer and am trying to get it all dialed in, and
running properly, but if I need to be careful of feed direction I would
appreciate the help.

So if grain direction matters, which way should I feed and how do I
tell which direction the grain is going in along the length of a plank?
I know this is probably a very basic question, but I don't know the
answer.

Thanks in advance for the help.