Personal Mail (Or PM) is a way contacting other members of this board, by sending a private message. To access PMs, look along the top (underneath the logo) and you should see something that says "you have # new messages". Click on this, and it will take you to your inbox. Here you can view all of your messages that have been sent to you.
To send a personal message, click on "New PM" just above your inbox. Then type the usename of who you want to send it too, your message, and then click send.