I'm unsure if you're having difficulty with a particular aspect of the exercise, so I've just guessed at some potential problem areas. Most importantly, being able to follow along with what an instructor is doing is one thing, and being able to do it on your own is something else entirely. The struggle that happens when the video ends and it's time to do the work yourself is important, and it's okay if you don't nail it right away. The important thing is that you try, even if (especially if!) it's hard.

If you're having trouble drawing boxes on your own, watch the video again. This exercise essentially provides a formula for how to draw a 2-point perspective box, and once you understand the gist of it -- draw a vertical line, run the top and bottom to both vanishing points, add two more vertical lines, etc. -- then you will have the freedom to apply that formula elsewhere on the page by choosing where the first vertical line will go and how tall to make it, where the next two will go, and so on. It's like learning a math formula. Once you know how the formula works, you can put in your own values and solve any problem.

If you're getting lost in the jungle of lines that arise as you draw multiple boxes, just try your best to keep track of the lines that are relevant to you at this moment and don't get distracted by the lines of other boxes you've already completed. You will develop a better eye for ignoring or focusing on lines with practice.

If you're hesitant about having boxes overlap, just go for it anyway. Overlapping boxes provide a good sense of depth, and the bunches of lines all together will get you more comfortable with focusing on the lines that are important.