...annotation is something we all do all the time and can include everything from footnotes to criticism, graffiti to fan fiction. What is social media but spaces where people annotate texts and images, the digital margins of our daily lives?
Thought about in the way of the quoted passage above, annotation is likely an activity you're already comfortable doing.
It is also a very helpful part of the active reading process, to keep you engaged with the text as you're reading it closely. This video emphasizes that role of annotation, with a few how-to tips.