У вашего броузера проблема в совместимости с HTML5
AutoCAD Stair is using simple command and classic design. The important command is like array, extrude, pedit and boundary.
More video tutorial
AutoCAD 3D House Modeling: https://www.youtube.com/watch?v=FERNTAh5s0I
AutoCAD 3D Guitar: https://www.youtube.com/watch?v=Uf2-bP4S_XE
AutoCAD Tutorials Playlist: https://www.youtube.com/playlist?list=PLjyiWW2QlmFwXcacgfcrwHWU2jNMYd37C