Stickies, as the name suggests, is an application readily available on your Mac to let you stick your thoughts - in a form of small notes - on your Desktop.
Stickies reside inside Applications → Stickies.
Not only limited to making notes, but with Stickies you can also perform several tricks, such as embedding picture, scrolling down notes, making stickies translucent, and many other tricks.
Upon continuing reading this article, you will see several tricks for using Mac Stickies.