Lots of people think using a layer mask is only for the advanced Gimp users, fortunately this isn't the case at all. Let me explain you the basic usage of layer mask on a easy to follow step-by-step example.
If you want to start learning PHP and MySql, the first step is to setup complete environment on your local computer. This will include Apache web server with PHP support and MySql database server.
If you don't want websites tracking you, and you don't want the pages you view to be saved in browse or search history, you need to active the incognito mode and this is what you need to do.
Mac OS X Moutain Lion and its Safari web browser sharing options allow you to share and send any web page vie email as a PDF attachment in a matter of two clicks.