Easiest way for me...
Click on Members name, their profile and summary page will come up.
Lower left of screen is Actions, below that click on send personal message.
That will bring up the New Message page (PM). The person you are sending it to, their name will appear under the To: box, you can add others here if you want to send it to more then one person.
Below that is the subject field, and below that is where your message goes.