Its never been easier to learn how to doodle:
1) open a template from Template Gallery,
2) doodle over the template with an Apple Pencil (best option) or your finger,
3) hide the template to see how good your doodle is,
4) save your artwork in Photos,
5) add any photo from Photos to the Template Gallery and doodle over it like in 1)-4).
Enjoy doodling :)