The GIMP, as I have mentioned in an earlier post is a powerful, open-source, free graphics editor. It is very powerful, but difficult to learn.
The GIMP gives you a toolbox with many simple tools, but you can combine them to create some fantastic effects. For example, here is something I created using text in the Old English fonts I have on my computer (I think they are from Dover's Old English collection) .
This involved many steps. It required duplicating images, adding blurs, using the "bump map" filters, adding random noise, and much more. I would never have guessed how to add these elements together without reading The Artist's Guide to GIMP Effects: Creative Techniques for Photographers, Artists, and Designers.
This book consists of step-by-step tutorials that show you how to use the basic elements in the GIMP's toolkit to create various artistic effects. After working many of the exercises in the book, you will have acquired an understanding of the process of creating digital art, which you can apply in new and creative ways. It is a little expensive, so I would suggest buying it used or asking your library to borrow it from another library for you (assuming that they don't have it in their collection). It is definitely worth taking a few hours to work through the exercises.