Community Server uses a feature called "conversations" much in the same way that you would send a private message to another user on other forums you may frequent.
However, with Community Server, privacy concerns are a little stricter. If you want to start a conversation with another user, you must first add them as a friend. Once they approve the request, you will find a link that says "Start Conversation" below their avatar when you pull up their profile.
Another alternative is to make yourself open to conversations to any users, not just your friends. To do this, do the following:
- Open up your profile by clicking on your user name at the top right of the page.
- Click the "Edit Profile" link that will be in the middle of your bio page.
- Click on the "Site Options" tab.
- Scroll down a bit until you come to the "Conversations Configuration" section. From here, change the option to "All Users." Conversely, if you don't want any kind of private messages, you can change this option to None.
Doing this will allow others to contact you, and once the conversation is started, you can continue to chat back and forth through it.
For the record, I've just update my profile to allow conversations from anybody. Feel free to contact me directly at any time if you have any questions/comments/whatever.