When you have completed a document, you should save it to retain it permanently. To do so, click on the ribbon command File | Save 
.
Tip: This command can also be found by default in the Quick access toolbar below the ribbon.
If the document does not yet have a name, Presentations automatically prompts you to assign a file name to it before saving it.
Saving under a different name or in a different location
Presentations also has a ribbon command called File | Save as. This also saves your presentation, but you can first assign it another name or select another folder in which to save it.
Saving in a different file format
You can use the ribbon command File | Save as to also save a presentation in the file format of another program. To do so, select the desired format in the list Save as type. For more information, see also Working with other file formats.
Saving all open presentations
If you have multiple documents open at the same time, you can use the ribbon command File | Save all to save all of them at once. Presentations checks whether the files have been changed since they were last saved and saves only those that have been changed.