Grouping and Stacking in Bridge
If you have multiple shots of the same subject and would like to be able to group them, image stacks are a good idea. Either Shift-click or Command-click (PC: Ctrl-click) on the images that you would like to group and press Command-G (PC: Ctrl-G). This will create a stack of the images. You can expand the stack by pressing Command-Right Arrow (PC: Ctrl-Right Arrow) or collapse the stack back into itself by pressing on Command-Left Arrow (PC: Ctrl-Left Arrow).