Presumably you refer to this "back arrow" seen within the iPhone Notes App:

This button does not "save" the open note; changes within Notes are automatically and continuously made as the "open note" is edited by the User. Instead, this button is used within the iPhone Notes App to return from the currently open note to the Notes listing.
This button is not seen within the iPad Notes App - as, with the iPad's much larger screen, the return-button is unnecessary.
For iPad, the Notes list is simply accessed at the left of the Notes window. The Notes list is exposed or hidden by tapping the "twin arrows" button at top left of the Notes window.
