Can't Ctrl. + click a new vertex

Hi,
in my endeavor to get Blender under my control I came to where I am supposed to Ctrl. click a new vertex into my mesh, or rather extrude one out of it, but no matter how much I try, nothing happens.
I have my Blender 2.79 set to LMB-select. Could it be that has something to do with it?
Can somebody please help me?

P.S.: to my biggest embarrassment I got the version wrong.
I have Blender 2.78…