that is a big subject. Digital art in reference to something in particular or a specific style.???
I work with top end editing software ( Photoshop, Illustrator, Xara Extreme, 3ds max, Maya, Flash, Zbrush, etc. ) and the type of work i am doing will aid in what i choose for rendering and editing work i create.
I draw by hand, paint and so forth. but i also create from scratch digital drawings, sketches and 3d work depending on the project.
Such as a drawing..working digitally with Photoshop often using a drawing tablet ( wacom ) see their site..
http://www.wacom.com/intuos/
i use the medium tablet for most of my digital work. Great product would recommend to anyone serious about their digital artwork.
Practice and study of what is necessary in the industry are essential.
There are many places you can learn for free online.
Yahoo or Google ( both is best ) for topics you are interested in learning more about and go from there.
cheers