Groups allow you categorize actions, such as Feature, Bug, Design, or Meeting.  Anything you want.  Groups are different than Milestones in that they are not time oriented.  Each group has a name and a description.  The name is displayed with the action and when you select the group for an action.

Additionally, you can select a color for the group.  The color is displayed next to each action of that group so you can easily identify common actions.

You can filter actions by group within the "All Open Actions" and "All Closed Actions" listings.

Creating Groups

You can create a group in the Groups section under the More tab.  Simply click the "Create a Group" button and the Group Dialog will appear.  Enter the properties of the group and click Ok.