A Classmates Email is a private message sent directly to the recipient's Inbox. To check the Classmates Email you've sent, click your name/photo in the orange bar at the top of any page, go to your Inbox and click the Sent tab.
Profile notes, on the other hand, allow you to post notes on another member's profile or your own profile. A published note is available for anyone to see. To view and post profile notes on your own profile, click your name/photo in the orange bar at the top of any page, select My Profile and then click Notes.
When you visit someone's profile page, you'll see the option at the top of the page to Post a Profile Note by clicking the chat icon or Send an Email by clicking the mail icon.