Well to talk to people in the same map as you they usually talk in "Shout" or "Yell" so that everyone can hear it.
As for linkshells youd need to find a few recruiting usually you can find them in game if not reddit or the official website can help you with that.

My names Gavin Laville in game and im on behemoth, id recommend joining a small linkshell or FC instead of a huge one until youre ready to raid (if at all) cause bigger linkshells tend to have their newer members ignored imo