You won't be able to send private messages until you've been with us a little longer, but you can receive them.

Have a look at the top right of the page. You'll see your user name and some other information.
This is what mine looks like:

Welcome, Koala77.
You last visited: Yesterday at .... (it gives a time)
Private Messages: Unread 0, Total 0.
Change Mood:
My Mood: Change Mood(I don't have one set at the moment)

If you click on the Private Messages, you'll be taken to your Inbox.

I hope that helps.