By default, SketchUp has just one layer, the Default Layer0
The DWG file you were handed brings along 11 more layers.
SketchUp’s layer system does not isolate geometry. Layers in SU only control visibility.
SU’s sticky geometry will meld into an unmanageable mass, regardless of its layer assignment.
SketchUp utilizes a ‘container’ system comprised of Groups and Components to isolate geometry.
A Group or Component (aka groups) may be assigned to a new layer to control their visibility as needed.
However, the primitive raw geometry (Edges and Faces) within them must remain assigned to Default Layer0.
Thus, the Default Layer0 must remain the Active Layer to avoid creating geometry assigned to other layers.
Moving the Active Layer away from Layer0 as shown in your screenshot is a path to modeling mayhem.