Grouping allows you to link individual elements so they move and resize as a single unit.

In this example four separate frames have been dropped on the canvas...

Image by Kent Smith

then arranged in a postcard style, with a text element added.

These frames can be grouped together so they can be treated as one single unit.

Select all images you wish to include in the group. Either mouse-down-and-drag a marquee to cover the entire group, or use Ctrl-click to multiple select the images one at a time.

 
Right-mouse-down on any one of the selected images -- a pop-up dialogue of available selections will appear.

 
Select GROUP SELECTION from the list of options.  Alternatively, you can hit "G" on your keyboard to apply the group attribute to the selection.

You will now notice that there is a demarcation box surrounding the group. This defines the frames that are within the grouped section.

The handles will allow you to resize the group as a whole, and you can rotate the group as well.

Grouped elements have been resized and rotated.

To add additional elements to the group, simply repeat the steps above with the original group and new frame(s) added to the selection.

If you wish to further edit elements within the group, hit Ctrl-G on your keyboard. Your group will continue to be grouped; however, elements within the group can be selected and have new attributes applied to them.

To undo grouping, select the group and hit "G" on the keyboard OR right-mouse-down and select 'ungroup' selection.

To view which frame numbers are included in a group, then select the group and choose VIEW >> Properties>> Group on the menu.