This is an elephant which was draw on photoshop using only the brush tool and only 1 layer. I changed the size of the brush to make different lines and shadows. To make the elephants colours look realistic I used the eye dropper tool. The short cut keys to make the brush bigger or smaller are [ to make it smaller and ] to make it bigger.
This is an example of destructive editing. I have selected the sky by using the magic wond tool and marquee tool to select just the cityscape. Then I invert selected it to removed the sky. This is called distractive editing because you can not bring back what you removed.
This is an example of non destructive editing as no changes has been made to the original layer. The sky has been “masked”. This means there was a layer put on the selected area which in this case was the sky. You can always removed to disable the mask.