"We write ourselves notes when we want to remember things."
Translation:אנחנו כותבים לעצמנו פתקים כשאנחנו רוצים לזכור דברים.
Yes, הֶעָרָה "a remark" is more abstract, i.e the content of the note, you can make it verbally too. הֶעָרָה is etymologically a sort of "upwaker", which is a nice concept. With פֶּ֫תֶק you imagine more a slip of paper with writing on it. Both the writing and the object are "a note", I guess.