added first part of layer masks

_subsections/chapter04.org

@@ -9,6 +9,25 @@
 
 * Notes
 
+the purpose of the mask is to hide parts of the image
+
+** setup a mask
+1. select the text
+2. click on the mask button in the layers pane
+   - this will add a white square to the right of the text entry
+   - [[file:../_share/media/img/photoshop-beg-piximperfect/lesson3-1.png]]
+
+The concept of a layer mask is that
+- black areas are hidden
+- white areas are shown
+
+so select the layer mask and draw with black on the center panel to hide or show areas
+
+*** to hide and show the layer mask
+- hold the alt/opt key and click on the layer mask
+- you can also click on any other layer, or outside the layer mask to hide it
+
+
 * Playlist
 
 #+ATTR_HTML: :class playlist