To send a PM here's all you do:

Click on a post of someone to whom you want to send mail.  When you do, you will see a little envelope by their name.  Click on that envelope and a mail box will open up allowing you to type a message.

Type in your message and voila, you have sent a PM.  By the way, only members with VIP can send a PM.

You can go to the green "Mail" tab at the top of this page, then click on "Compose" on the left-hand side, and MANUALLY type in the handle of the person you are trying to contact.

It's that manual-thing that is soooo cumbersome