If you want to contact a member and see his name on a post, next to it is a pm button, click on it and it takes to to the User Control Panel, PM section.
When you have finished with your message, click submit.
The person you are contacting will receive an email telling him that he has a pm waiting in his inbox and a direct link to it.
Also when he signs in there will be a pop up notice telling that a PM awaits.
Yopu can check you outbox to see if he has received it.