Any new charts that are created by the program, plus any charts which are edited instead of being opened, must be saved to a chart database if you wish to use them again in later sessions with the program.
It is possible to save a chart by manually selecting Save options within the program, or alternatively any new charts can be saved automatically whenever they are created by switching this option on in the "Preferences" dialog, "Charts" tab.
For more information on saving charts see Saving Charts to a File.