In MantidPlot, you can save your work into project. Then when you run MantidPlot at a later time you can recover this work by loading the project.
A project consists of a .mantid file and a collection of Nexus files it refers to. For this reason, a project is put into its own folder when saved.
See also
MantidPlot:_The_File_Menu for how to save or load a project
Category: Concepts