Hello,
I'm a beginner and I need help. File is attached.

I do this:

1) I draw a rectangle of whatever shape.
2) I extrude that rectangle to get a solid (Question: Do I have to first make a planar (Construct->Planar) out of my rectangle to get a "real" solid?) Is there a difference if I use that function?
3) I draw another rectangle that is smaller in size that sits on the same z height.
4) I extrude "Rectangle 2 solid" into "Rectangle 1 solid" but with a smaller depth (z).
5) "Rectangle 2 solid" is now completey wrapped into "Rectangle 1 solid".
6) Now I want to subtract "Rectangle 2 solid" from "Rectangle 1 solid" with Boolean -> Diff

Problem: (whatever I do, tried over an hour to understand the behaviour)

I can't select only "Rectangle 1 solid". Always both rectangles are selected.
I absolutley can't select only "Rectangle 2 solid". Wherever I hover.

An help would be (very) much appreciated!

Thank you very much!

Best wishes,
Pierre