About the how-to send private messages:
Do you see in the upper right, four icons? There's like a silhouette of a person, and then a box with an arrow, and then a bell, and then a magnifying glass?
The box with the arrow is for conversations. If you hover or click on that, you can "Start new conversation". Do that and then put in the person's name you want to message, and that's a private chat.