I solved the lesson after 2 or 3 approaches.
And… My method was more or less alternative to that one in Lecture. I think my method is better.
I streamed a video. For your consideration,
Some explanations
on 0:32 selecting 2 FACES I merged them simply pressing F.
on 0:50 I selected the FACE again, switched to verticies (all 4 selected as they formed shape). Then pressed E (extreude) and Enter (the extruded vertices are at the same position).
Than I simply TRANSLATED them forward in snap to verticies mode. In one mouse movement.
After selected all I pressed again F. But I think that was overkill. Checked Normals later. All OK.
How do you like my method?