What you can do with several items

Wherethe Selected windowwhen the set contains two or more items
ButtonWhat it does
Six Level iconsLine up the edges or centers of items: by the left, right, top or bottom edge, or by the middle
Equal spacing ↔, Equal spacing ↕Space items evenly. The outermost ones stay in place. Needs three or more items
Flip ↔, Flip ↕Mirror the set about its center
Make a copyPlaces a copy of the set next to it
Group icon in the headerCombines items into a group. See How to group items
Trash can in the headerDeletes everything selected

The item's outer bounds are aligned, taking its rotation into account, not its center.