Adobe Photoshop is a program for editing and 'manipulating' photographic images. Illustrator is a program for illustrations. Flash is a program for animations.

Adobe makes a very wide assortment of image and graphic programs. Their functions complement each other, and even overlap somewhat.

If you worked as a graphic designer you would probably use several of them. They are designed to work together so, for instance, you can edit a photo in Photoshop and export it to Illustrator to use it as part of a diagram or flowchart or something, then export that into Pagemaker to design a page of an instruction manual.

When studying Graphic Design, you are taught to understand and effectively communicate your ideas using imagery, text, color, layout, etc.

Abode Photoshop, Ilustrator and Flash, are merely tools used to help you create your design and you are usually taught how to use these programs in Graphic Design courses.