":" runs Emacs functions. Some commands from Vim have been added, but not all of them. If a function with the same name as a Vim command already exists in Emacs, it's not replaced. I'd imagine replacing the default Emacs functions could break things in weird ways.
:cd runs the Emacs cd function which behaves differently than Vim's :cd.
To get the equivalent of :tabnew, you'd have to use :buffer [name] and give the new buffer (Emacs's equivalent of tabs) a name.
Oh, I see, thank you. As I understand buffer name isn't the same thing as file path/name. So I can't really open file by pasting (Ctrl-r +) it path anyway, can I? Also, I only understood how to switch between buffers using that separate screen, not like "next/previous tab", and there isn't any panel that would show which tabs are opened now. But I think that's solvable, at least.
:cd runs the Emacs cd function which behaves differently than Vim's :cd.
To get the equivalent of :tabnew, you'd have to use :buffer [name] and give the new buffer (Emacs's equivalent of tabs) a name.