Samsung Galaxy Note 4 - Manual (Page 54)

S Pen features
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3
Write with the S Pen.
When composing a message in Messages, tap at the top of the handwriting field to
switch to drawing mode. A drawing will be inserted into the message as an attachment.
4
When you are finished, tap .
Writing in apps
You can write directly on the screen with the S Pen when using some features and apps. For
example, you can enter numbers on the dialing keypad or set an alarm time by writing on the
handwriting field with the S Pen.
If this feature is not activated, open the All apps screen, tap Settings → S Pen →
Direct pen input, and then tap the Direct pen input switch to activate it.