You will want to save your work both as final rendered images as well as Xml files. This section covers the latter.
The Library tab shows the currently opened flames. You will notice that the preview in the Library tab updates as you edit your flame. This updates the flame data in memory but does not save it to disk.
To save the contents of the current flame to disk, click Save current as xml. To save all opened flames out to a single file, click Save entire file as xml. When only a single flame is opened, these two functions have the same effect.
After the flame has been saved once, clicking save again will have a different effect depending on the Auto Unique Filenames option in the Xml Render Values tab of the Options dialog.