There are all sorts of graphics applications: business graphics for converting numbers into graphs; clip art applications for making personalized greeting cards and the like; art applications for creating original drawings; and more.
Business graphics applications take numbers from spreadsheet applications (or numbers you type at the keyboard) and turn them into graphs and charts. (Obviously, it's a lot more convenient if your graphics application works with your spreadsheet application.)
You can use the charts and graphs you create to illustrate reports and presentations or just to clarify statistics in your own mind. If you're going to be using your graphs for presentations, it's handy if your graphics application has a slide-show option, which lets you arrange several graphics in order and changes slides for you after a prearranged number of seconds or with a keystroke. For a large audience, you'll probably want to print your graphs onto sheets of acetate for use with an overhead projector.
If you like to make your own greeting cards or garage-sale posters, or illustrate your correspondence, but don't think you have an artistic bone in your body, clip art is for you. Clip art applications come with a library of illustrations: animals, musical instruments, sports equipment, seasonal symbols (a turkey, a firecracker), and so on.
You combine the pictures with a personalized message printed in your choice of type style to create greeting cards, stationery letterhead, banners, posters, flyers, birth or wedding announcements, party invitations, or anything else that lends itself to illustration.