Game Notes is a pre-installed feature which allows you to write notes about the current paused game. These notes can then be transferred over to Miiverse as a written message. It is one of the five multitasking applications accessible from the Home Menu.
Game Notes can be used when a game isn't running, this is deemed useful if the users wants to write a general note. A screen shot of a game can be saved with a note if the game is running when Game Notes is opened. This is done by exiting the game via the Home button the selecting the yellow icon in the multitasking apps. Notes can also be exported to the camera roll.