Start dragging on the page frame (the dark grey area around the selected page) or on an area that does not already contain a widget other than the background.
All widgets that are contained in the blue box after dragging will be selected.
You can now align, copy, paste and group everything inside the selection.
Use the group icon to group or ungroup selections of widgets.
The group/ungroup icon will become available once you have selected more than one widget.
Groups will be clearly indicated by a border when selected.
In order to edit widgets in a group, they must be ungrouped first.