With just one click, a new email opens and the body is populated with your notes. This is the best way to send notes if you know someone doesn't have OneNote.
Now if you're sending your notes to someone who you know has OneNote, it's probably a good idea to sent them as an attachment so they can open and modify them.
This time, notice that there are a couple of attachments. The first is the OneNote file, and the second, as it says in the message body, is a file that is viewable in a webpage.