Grouping and Ungrouping Objects
Related objects can be grouped together, so that they always become selected and move as a whole. When you select one object in a group, all of the other objects in the group are selected. When you move one member, the rest come with.
To group objects together:
Select all of the objects you want to group.
Click the Group button in the toolbar, or choose Group from the Arrange menu.
Now when you select or move one group member, the other members are automatically selected or moved too.
To ungroup objects:
Select the group.
The click the Ungroup button in the toolbar, or choose Ungroup from the Arrange menu.
Now you can select and move the objects independently.
You can cheat a little and still manipulate grouped objects individually without ungrouping them, if you really want to. Hold the Command key while selecting a group member to avoid selecting the rest of the group.