FastFig automatically saves your work, you don't have to worry about it.
However, if you want to be sure, use instant save.
For Instant Save at any time Press 'control - S' ('command - S' in OS X)
Hint: Label your documents in the upper left corner of each page, to keep notebooks organized.
You can change page names at any time. You can also change your notebook names from the main application window.