You can use a small circle on top of a circle skirt for an overskirt. Also you can cut a slit in the front of a large circle or small circle over skirt and fold back the edges to make the overskirt third over from the left in the picture above. The straight skirt over skirt is made like a circle skirt but with the straight skirt piece.
You can use the over skirts on top of a mermaid skirt style dress.
The straight skirt over skirt can also be used as a skirt on its own.
However, since it is rather short I usually only use it as a skirt on dolls like Monster High and Ever After High. I place it around the lowest part of the top for a drop waisted look and to add a little more length. Also, depending on the overlap in the back it can be a bit breezy for the doll so adding another piece of paper in the back can be a good idea.