While I don't fully understand your question (language barrier might be a bit of an issue), I'll take a guess, and we'll see if my answer is of any help here.

I think you might be asking about something related to how, in earlier exercises, I've talked about avoiding trying to cut back into the forms you draw, as shown here. When working with organic subject matter, it pretty much always causes students to flatten out their drawings. For geometric construction, like the stuff we deal with in this lesson, that is not the case. It's actually much easier to work subtractively for stuff like this, because when dealing with these bounding boxes that surround our objects, it's easier to understand how we'd cut into them in three dimensions, rather than just as shapes on the flat page.

That said, looking through your drawings, I think there are some areas where you're skipping steps, which does cause some issues.

Before I get to that though, I want to mention that your form intersections are generally looking good, except for one issue - do not trace back over the silhouette of your forms. Doing so results in really wobbly, stiff, hesitant linework which undermines the solidity of the forms, making them appear somewhat more flat. Remember that line weight should be reserved for clarifying how specific forms overlap in localized areas. It should be applied using the ghosting method, achieving a confident execution, and not to reinforce the entire silhouette of a form. I talk about this in the instructions for this exercise, here.

When it comes to your own drawings, I really would have preferred if you'd have sticked to the same pen throughout the entirety of your instructions. I did mention that you shouldn't be switching pens - I know I wasn't specific in talking about colour, but I want students to treat the constructional steps as being part of their drawing, not as being something separate. You asked in your comments whether it should be "more like a guide" like the circle in the hibiscus demo.

In truth, even in the hibiscus demo, we're creating structure/scaffolding upon which to gradually build up our drawing. It's true that the circle wasn't going to represent something that exists in the flower itself, but it was still part of the construction itself. The whole drawing is just a construction - there's no separation between a "final" or "real" drawing, and the steps we use to build up to it. Every single drawing throughout this entire course is just an exercise in spatial reasoning.

Now you did adhere to this in some of your drawings. In this object, even though you used multiple colours, it doesn't look like you were redrawing anything, and as a result the construction came out feeling quite solid.

Conversely, if you look at this nail clipper, you appear to have started with a box, and then you drew the nail clipper in its entirety within that box, rather than breaking it into a series of smaller, simple forms, and gradually building your way to something more complex. You started with a box, and jumped straight into the far more complex object. That is not how this lesson should be approached.

For example, looking at your guitar, you went from that big enclosing box straight to a lot of very curved lines. As I demonstrated on another student's work, you should instead go from the larger bounding box to a series of boxy forms that define the general structure of the guitar. From there, you can round out the curves.

Another demo I have to help convey this is this mug. Based on your approach, you'd jump in and just draw a curving tube for the handle. Note how I instead break it down into a structure made up of straight, rigid forms, and gradually build up its complexity until finally I'm ready to round out those curves. We can actually compare this to the handle on this kettle.

One last thing I wanted to call out was in this stool. Here in your orthographic studies (the top and side view), you used the diagonals method to find the centers, but you didn't do so for the side of your actual construction. Instead, you appear to have estimated. In this lesson, you should pinpoint everything as exactly as you reasonably can. After all, you're given the tools and techniques to find the center, to mirror a measurement across the center, and so on. All it requires of you is that you invest the time to use those techniques. Right now you do so to varying degrees, but often are still inclined to jump in and approximate things, or draw by eye instead of constructing things as specifically as you otherwise could.

So, I'm going to assign some revisions. I'd like you to complete each drawing entirely with black pen, avoid redrawing/tracing over existing marks, and build up your construction in far more steps, building more gradually towards the end result, rather than jumping over important stages.