Well I don't think it is called screwing, in hungarian engineers yews the word "shear" for it I don't know why. To be honest I don't know what control+left mouse button does (seems useless), but you have two other options to do this: 1st clipping (I'd probably do this because i always forget the 2nd one is exist for brushes as well, I yews them for patches) 2nd using vertices, you assign the brush, then press "V" 6 points are going to appear, you have to assign four of them with shift+left mouse button. (Judging from the video, you have to assign two point in the ZY dimension, you will assign four because the other two are hidden for your eyes, or you can just assign any point 1 by 1). Then switch to "Translate" mode with the key "W" and move the assigned point with it (the blue arrow in ZY dimension). (Logically if you were already in translate mode pressing W will switch back to the previous mode) You can do many weird things with vertices, if you want to do something impossible gtkradiant simply won't let you do it.
And next time please give me timed youtube links, or if you don't know how to make them tell me which part I need to see.