MPS questions about transformation menu's

I also asked the following questions on MPS slack:

I found and followed a video about transformation menu’s (Vaclav Pech: Transformation Menu Language - YouTube), but it only explains the side transformations, and I need an explanation about the other transformation menu possibilities (actions for completion, including menu’s, etc), and also about substitution menu’s. Where can I find video’s or other explanations about these subjects?

In particular, I have a concept with a reference to an existing node, for which a referent cell is in the editor of the concept. Default it makes it possible for the user to select one of the existing nodes as the node to refer to. I want to add the possibility for the user to add a new node and refer to this added node, via the completion menu. How do I do that with transformation menu’s?