Put your mouse cursor on the line dividing the two layers you just made (the lower layer with your main image and the upper layer with the "gray fuzzy stuff" on it.) Your cursor turns into a Pointing Finger Hand thang (A). Now hold down your ALT key (or MAC equivalent) and you'll see the cursor turn into a funky overlapping circle thing with an arrow pointing out the side (B).
Right CLICK! (C) The upper layer jumps to the right with a nifty angled arrow pointing to the Object layer below.
Note: to CANCEL a Clipping Mask layer just re-click on the dividing line again and it will toggle back and forth.
Quelle:
Ist halt nur für die Clipping mask, wie man eine Bildberechnung macht und brushes setzt solltest du eigentlich wissen.