Negative space drawings are made by only looking at what is NOT there. There are no internal details in the objects, because that is not what is being drawn.

This is aided by the use of a viewfinder, where the space between the object and the frame can be clearly seen.  It's best to have the subject of the drawing touch your viewfinder on each side; that will provide another negative space for the outside shape of the subject.

I'm not a fan of the shading (so please don't do that) but I think it helps you to see that there are no deatils within the subject of the drawing—you are outlining only the negative space—what isn't there.

See the examples below of two stools, a chair, and a handtruck from: https://scienceleadership.org/blog/negative_space_drawings_and_cut-outs