What are My Saved Themes and How can I use them?

Your Saved Themes are shown in the Design > Theme Editor > Saved Themes section of the control panel. These are either themes that you have created and named yourself using the Theme Creator or they have been imported from the Public Theme Library.
How to Save - Theme Editor - Menu
The "Save Now" button will allow to save your current theme and the design choices you have made on them.
The "Library" button will show you all the designs you have saved, here you will be able to select and restore any of them.