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.
Pretty nice looking and simple to create effect, where we turn everything into pixels except the selected part. My car will end up looking like it's trying to escape out of the pixelated background.
If you found yourself in a position where you wanted to crop a certain photo into a perfect square but you just couldn't figure it out how, than this tutorial is for you.
In this simple tutorial suitable for the Gimp beginners as well, we are going to manipulate a photograph of standing still car to make it look like it's passing by real fast.