Welcome.
We have two different ways of chatting. Chat rooms and forums. Chat rooms are real time and forums are a post and wait.
To communicate one on one (PM) depends on if you're in chats or forums. For the forums you can go to someone's profile and message them from there. Or if you see someone in a thread clicking their name gives you options. Also by adding someone to your friends list you can find them there.
For the chat rooms you have to pay to open up some features, but since you joined in 2013 you may have been grandfathered in.
Different people respond in different ways to getting PM's from strangers, so it's usually a good idea to build a little familiarity with them first, just to be safe. There are those that dislike messages from strangers.