Digital Art is an artistic composition that relies heavily on the use of technology in its creation. Digital Art comes in many forms, most often it's either solely computer-generated, drawn using various types of software, or digital paintings sourced from photos.
To start with digital art, try to draw by following existing sketches or images. As you exercise, you will develop your ideas and thoughts, learn about proportion and perspective, and gradually develop your own techniques.
Studying tutorials from other artists can also help to develop your technique. There are plenty of tutorials on various drawing subject available on the Internet.