Practice
Shall we practice a bit more?
Let's start with accessing the dom: Exercise 1.
The goal is for you to attempt Lessons 1 to 5. If you feel courageous and remember your JS from the introduction to programming, you can attempt solving the Exercise: Tree Walker, but it isn't within the scope of this exercise.
Once you're done, what about getting some practice around manipulating the DOM?
Finally, let's go back to our Chrome DevTools and do another of its tutorials: Viewing and Changing the DOM