Obtain some graphics programs. Adobe Photoshop (or Adobe Illustrator) is the best, but Corel Paint Shop Pro is also a fine program. If you cannot afford to purchase a full package (such as Adobe Design Premium), you can download individual programs at the official websites where they are sold. Adobe gives you a 30-day free trial, which is a decent amount of time to get your start in learning a new program.
Invest in taking courses at your local college or university. Digital design is usually offered as a continuing studies course package, and many schools allow students to register for and take single classes, so you won't have a problem if you only intend to take one or two courses. Classes should last at least five weeks, and will be around three hours long, so you will get a good start in learning the programs.
If you do take classes, be sure to purchase any textbooks and educational CDs your instructor might recommend or require. These are excellent to use as you learn the program, and they help you as you work in a hands-on manner. It is a good idea to purchase books even if you don't take classes, as this makes it easier to learn the programs much faster than you would with just the programs alone.
Practice using the graphics program as often as you can. The best way to learn is to keep at it. Practice and persistence pays off in the long run, and you can create and save your own graphics. Study them often. You will notice an improvement in your skills with time and patience.