Objects are "stacked" when created - each object is created "on top" of the previous object. This sometimes has no visual effect, but stacking order can matter in the case of images and filled or hatched objects.
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- Select the circle and select Bring to Front.
2. The circle is now at the top. This, in effect, changes the creation order - the circle is now considered the most recent object. (You can verify this by pressing F7.)
3. Select the circle again and select Back One. Rather than sending the circle to the bottom of the stack, it moves just one level down.
If you change the stacking order of multiple selected objects, the selection set will move as a whole. The relative stacking order of objects within the selection set is maintained.