Sticky Notes View by Dreamsorcerer is a GNOME Shell extension to place notes on your overview mode. You view/hide it by clicking its icon on the left-vertical panel.
Follow our instructions about installing GNOME Shell extension. Once installed, you will see its icon on the most bottom of the GNOME left-vertical panel.
Enable overview mode (by pressing Super key) then click on the yellow icon (of Sticky Notes View) then a yellow note will appear. Once you write some text on it, a new yellow note will appear beside. To delete a note, simply click on the close button on the top-right corner of the note.
To disable or uninstall this Sticky Notes View extension, use GNOME Tweak Tool program.