It can be a form or written communication that is sent or received.
He received a note from his boss.
The students were caught sending notes to each other during class.
A note is also something that you receive as a payment or spend when shopping:
"This note is legal tender for all debts, public and private."
(The above statement is found on American currency.)
The word "note" is part of the compound word "notebook." Do you have a notebook? It’s a good idea to take notes in a notebook when you study English on this website. Writing answers to exercises and quizzes will help you remember what you have learned.