How to contact a member?

How do I send a message to another member?

a) post a message in a chat room that you see them in (type their handle/user name and they'll see your post in a colour different from the rest of the posts), or think that they visit (but, they may miss your message)

b) send them a friend invitation. if they accept, it's then easy to open a private chat between friends

c) chat with them during any games you play