I was writing an article when I for a couple of minutes procrastinated — Then I stumbled into this awesome website.
Apparently, it records your screen and turns into a step-by-step guide (I already tried it, and it works perfectly)
You can make small modifications to it, and when you are satisfied you can download it as a PDF file, upload it to Gumroad or Payhip, and start selling.
NOTE: It’s free unless you want to record something outside of your browser. For instance, if you want to record a word document, or if you want to record within Adobe Premiere Pro.
You can check it out here