Question

difference between save & open.Also New & open.

Answer 1

Save - refers to the document which you want to save after doing some
work in it.

Open - Open option helps to open the saved file.

New - Option helps you to work in a new sheet.

Open - helps you to open the saved file.

Answer 2

Save -  To write (save) the contents of an open (and working) document in the application (from main memory) to a file on the current disk drive, with the same name as the opened document.

Open:  To open (read the contents of) a closed document file from a current disk drive, into the main memory (into the application software window), for viewing or editing purposes.

Save =>    From application (main memory)  to Disk drive. 
open  =>  from  disk drive  => application in main memory

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New :  It is the option to open a blank new document/spreadsheet/presentation in a new window or the current window.  The new document is only in the application (main memory)  until it is saved.

Open:  It is the option to open (read the contents of) an existing document on a disk drive.

   New =>    fresh blank document in main memory (application)
   Open =>  from disk drive into an application main memory