Doodling

Before someone tries to learn how to doodle he or she needs to understand what doodling actually is. The word doodle comes from German, and referred to a person who was a fool, or who was simple in some way. The modern meaning of the word, referring to small drawings done idly while one thinks, came about in the 1930s and might be connected to the word dawdle for someone who's wasting time. 

All of the history aside though, a doodle is nothing more than an unfocused or unconscious drawing, typically made while one's attention is supposed to be focused elsewhere. This is why doodles often show up in the margins of notebooks or on sticky notes at work; people who are tethered in place and stuck listening to a phone call, lecture, etc. will pick up a pen and begin to make small, unfocused drawings. These are doodles.