As you can see, I like to start telling the story of painting with some global issues. It will be a while before the first stroke is made. Digital Painting is no different than "wet painting" in that you have to gather supplies, lighting, brushes, cleaning techniques... neither is a sport that can be done without preparation.
One of the most important things is to decide WHAT files to save and WHERE to save them.
About WHERE...always save your files in Two places. Believe me "XZ!!X" happens and you will be glad your paintings are still able to be found. I back up my computer once a week with Acronis. It takes a LONG time because it writes the entire drive structure. "I do's it the way I see's it!" could be their motto. http://www.acronis.com/