First ensure you are signed into your member account. Then navigate to "Messages" either with the mail icon shortcut on the orange member bar or the tab in your "My Profile" area:
Once in messages you can read new mail in the Inbox. Check your sent history in the Outbox. Manage your Contacts and Ignore lists. And you can select "New message" to send a message to another member:
Once viewing the "New message" you can enter a subject, create and style content but first you will need to "Select" the members you wish it sent to by hitting the "Select" button:
Next a window will pop up. Please ensure your web browser does not block this pop up window. If it did block it even after you told the browser to allow yo may have to navigate away form this page and then back again.
Once you can see the pop up "Select user" window you can choose form contacts already in your contact list, friends, or search for new names of members you are familiar with from the Bullboards:
Note the option to add a member to your "contacts" or to "ignore" using the little people icons to the left of the members name.
After you have selected the contacts and are happy with the contents of the message simply press send.