This help article covers Viewing and Sending Private Messages.
Public or Private
Many things are appropriate to discuss openly on the website forums. You might think no one else could care about that old house, or the photo storage boxes you found you a good deal on, but you would probably be wrong. If there is a chance information, no mater how trivial, might be of general interest, we urge you to keep it public. But there are times when things are best kept private.
Private messages can be viewed from the Inbox section of the "User Menu." If you have messages waiting, the Inbox menu item will change color, and show the count of waiting messages. This is a sample Inbox view:
Even if a user has elected to not publicly share an email address, private messaging is an available option. The Private Message option is commonly called "PM." PM buttons are available in many places. Click the PM button and a PM Posting screen will open, where you can write and send your message.
Also from the Inbox there is a "Send" button. Click on this button to open a PM Posting screen. This will include a drop down list, where you can pick the intended recipient.