Saving and staging is the section after you have your project in a place where you're ready to watch it on your EEVO app. You'll find these options up at the top left of the composer under the "file" section.
Staging makes your current build available to the EEVO app without saving your current build on the composer. You can save your composer session if you wish to keep your current build, without updating what's viewable in the EEVO app. Staging your narrative will let you see the current build on the composer on the EEVO app, but won't save your progress. If you wish to save your composer session and overwrite the version available on the EEVO app, you can press save and stage.