The readings come from Learn to Code HTML & CSS: Develop & Style Websites at https://learn.shayhowe.com/html-css/.
Some students prefer to do the readings before the lecture videos - they find it easier to listen when they recognize some of the words I am using. Some students prefer to do the readings after the lectures so that as they read they can connect it with what I said. Personally, I would suggest that you do the readings before AND after the lectures.
But no matter which method you chose, make sure you do the readings before the quiz. They go into more detail than my lectures and many of the quiz questions come directly from the readings. Also, make sure not to read the entire lessons for 8, 9, and 10. They go into CSS which we are not covering in this course. (CSS is the next course in this series.)