Be cognizant of the Block's Workplane (Coordinate System) and the current active Modelspace Workplane (Coordinate System).
Attached is a TurboCAD Drawing File I created that can be used for some experimenting and learning.
In it, there is a Block named "Orientation_Cube-1". All sides are labeled with the first Letter of where those sides were/are when I created the Cube on the World Workplane (F= Front; R= Right; Ba= Back; etc.).
That Block's Insertion Reference Point is located X=0,Y=0,Z=0 (World Coordinate System).
In Modelspace there is a Solid Regular Dodecahedron
Turn on your User Coordinate System icon... set it to "Show".
Set the Modelspace to any of the Dodecahedron's 12 Facets, using Workplane by Facet.
Insert the Block into Modelspace*, and you will see that the Cube's bottom facet is shares the same plane as that of the current Workplane facet, and/but the orientation rotates such that the Cube's inherent Coordinate System aligns with that of the respective axes of the current active Workplane. Just click on the just-Inserted Cube Block, with the 3D Selector active, and you will see the Block's Selector Rotation Bars are aligned with that of the current Workplane.
Repeat for other Facets of the Dodecahedron.
Anyway... Maybe if you play around with this some it will give you some sense of how this all works.
*To Insert the Block exactly in the center of the 5-sided facet, I:
>After having set the Workplane by Facet, inserted a 3-Point Construction Circle, Vertex-Snapping to three of the 5 vertices of the polygonal facet.
>Activated the "Center" Running Snap.
>Dragged the Block out of the Blocks Palette, into Modelspace, and hovered over the Construction Circle, until I saw the little "Center Snap" indicator, then clicked.