A daily note is a text written for a specific day. Once written, the text is attached to that day. It does not have to be the current day, that is, you can write a note to save something that happened on a day that has already passed. The important thing is that the content of that note is forever linked to that day in question, and you can consult it later.
On one hand, writing a daily note allows you to write down something that at that moment has caught your attention, something that you want to put down in writing, something that you do not want to forget.
On the other hand, it allows you to re-read whenever you want the notes you wrote that day, providing you with a record of what you have done during the day. This daily log gives you visibility into the small steps that you really make every day and, with a broad perspective, shows the path followed until today.