Users groups, or simply groups, is a way to group several items together. You can even group another group, making it possible to build a hierarchy of items which can be moved, rotated and modified together as one item. To use the group feature, simply select an item, then tap the group icon on the mini toolbar. This will put you in group add/subtract mode - any item you tap now will be added to the group. To ungroup an item from the current group, simply tap it a second time so it is unselected.
You can add groups of items to your own personal shelf, so they can be used multiple times and even in another plan.