Image of SofTutor is the fastest way to Learn!
From SofTutor for MicroStation 3D - Auxillary Coordinates & Commands
Topics & Keywords covered in this video are:

Using Saved Auxillary Coordinates On A 3D Element ACS Find Points Rec Plane
Auxillary Coordinates & Commands ACS Set Save Find Plane Element
ACS Plane Lock - To Draw Elements On 3D Planes Auxillary Coordinates Find Points Rec
Set/Save Auxillary Coordinates On A 3D Element ACS Find Points Rectangular Plane Name