Digital art programs vary widely, both in their capabilities and in their applications. There is no single, magical application that can do it all. The ones that come close are very expensive. They are the types of programs that are used by professional digital visual effects artists and game art and design creators.
If you are looking to eventually fill one of those types of positions, you should enroll at a specialized school for media arts. They can give you a solid footing in regards to the upper echelons of art creation and animation software. On your own, these programs can take years to understand, and much longer to master.
Lower level digital art programs are much easier to grasp, and much more affordable. Often they are available as demos and if you can find them that way, you should definitely try them out before you buy them. Some of these programs are Poser, Paint Shop Pro, and Corel Paint. This is far from a complete or adequate listing.
Working with Digital Art Programs
The only way to get good with digital art programs is to work with them on a daily basis, even through frustration. Some of the higher end programs are accessible, but you will feel like you are hardly using them for a long while. You should try out whatever programs you can, read reviews and comparisons, and then pick a couple that most spark your interest. Then use them all the time.