There are three main phases in the life cycle of a Presentation object: opening, editing, and saving.
Opening a presentation
When using the Slides Service, the first step is to load a presentation. Methods like SlidesApp.openById() and SlidesApp.getActivePresentation() load an existing Slides presentation, while SlidesApp.create() creates a new presentation. These methods return a Presentation object that represents the loaded presentation.
Once a presentation is open, it does not receive any further updates from collaborators. Presentations are usually opened at their latest version that has been saved in Drive. However, if a script is container-bound to a presentation, that presentation will be loaded at the same version as the accompanying Slides editor.
Modifying a presentation
Once a presentation is open, a script can read and modify it. Any changes that the script makes to the presentation are reflected in subsequent reads and modifications for the duration of the script execution.
Saving changes
After making changes to a presentation, the changes are saved all at once when the script execution completes, or when Presentation.saveAndClose() is called. After changes are saved, they propagate asynchronously to the user's editor, as if the changes were made by a collaborator.
After a presentation is closed using Presentation.saveAndClose(), it can be
reopened for editing using one of the presentation loading methods.