Another new feature to Exchange 2010 provides users the ability to manage groups from the web UI, if you are a group owner you can configure settings on the group and add members. However, if you do not own the group you have the ability to attempt to join the group. The manager configures the settings to allow one of the following

1. Open membership

2. Approval required

3. Closed

 I have created a group called Exchange2010_Discussion  for this demo 

The following steps out line how to join a group

 Click options in the top right corner

1. Click Groups from the menu 
2. Click the join button to bring up a list of groups that are available

   

3. Select Exchange2010_Discussion
4. Click the JOIN button
5. You will receive an informational message stating you have successfully joined the group

   

6. If you no longer want to be a part of the group ,highlight the group you want to exit and click the LEAVE button

    

7. You will receive a warning stating you are about to leave, select YES or NO 

   

8. Click closed on the successful group exit