A private group means the name of the group is not visible to the public.   Anyone can join, but they must know the group code.   You can join a private group by being invited into a group by someone already in it or you can register on your own and enter the group code which might look something like ACME1234.   (It's auto-generated when you create the group, usiing the first four chars of your group name, then randomizing four digits)

Let's assume you have been given a group code to join.   Here are the four steps required:

1.  Create an account  -- (it's free)

2.  After you login ... Click Select Groups icon from the Control Panel

3.  Click Join a Group

4.  Select Private, then enter the group code 

In some cases, you may have received a post card with the group code displayed in the corner... or it may have just showed up in some random email from one of your friends or posted on a website.   However you received it doesn't really matter... all you need to know is that it goes into the Private field.

If you're ready to get started... REGISTER