Anchor
You can display the Boolean and Facet toolbar by right-clicking in any toolbar area and selecting Boolean and Facet.
...
Note: 3D objects can also be combined using Boolean operations. See 3D Boolean Operations
...
The object created as a result of a 2D Boolean operation is considered a region. You can use the Selection Info Palette to determine the type of any object or objects you select. See Selection Info Palette.
Selection order can be important, because the properties (color, layer, etc.) of the resulting region are taken from the first object selected.