There are two ways to compose multiple shapes into one entity, groups and aggregations. They might seem very similar at first sight but represent different ideas.
A shape group is a collection where each single shape is still a shape on its own. For example, you can select a shape within a group and modify it like any normal shape. When you move or resize a shape of a group only this shape will be modified. The others stay untouched. On the other hand, when you click on a shape in the group all shapes of the group will be selected. When the whole group is selected you can move and rotate it as a whole. It needs a second click on a shape to select it for itself.
The idea behind an aggregation however is to form a new more complex shape out of simple shapes. The resulting composition represents one shape and not a collection of shapes as it is the case for a group. When you resize an aggregation all its constituent shapes are resized correspondingly.