Selecting Save or Save As... (depending on whether or not you wish to save to a new file) from the File menu allows you to save a Kst session. This contains all of the plot and layout information which Kst requires to reconstruct your session (as long as the data files used in the sessions are still present when Kst is reopened!). Browse to the location you wish to save the plot definition, enter a filename, and click Save. The plot definition will be saved as a *.kst file.