For these random doodles and notes, I used my Surface pen on Microsoft OneNote 2016. The tools consist of a simple pen and pencil with highlighters to choose from and a gradient of colors to mix and match. I'm a visual learner, so its easier for me to retain information processed thoughtfully and copied as visual notes.
No one really remembers the time when they realized what kind of learner they are, in my case I knew for a very long time that I was a visual learner. This was perhaps the reason why I enjoyed Trigonometry the most or that I loved sitting in my Chemistry classes--they are visually-stimulating subjects.
I've been using my Surface Pro 4 for a while now but just recently discovered how to keep and carry notes with this app called OneNote. You can find some of my screen shots, what do you think? Worth a try!