There are two image modes in graphic design: vector and bitmap. Vector (text, logo's, shapes, clip art, etc.) allows you to retain image quality as you enlarge and bitmap (photographs..) will lose image quality as you enlarge them. Resolution is another topic you need to have an understanding of, but right now I'm going to talk about the balance of vector and bitmap in the design industry.
Everywhere you look in magazines, posters, ads, brochures, billboards you will almost always see both vector and bitmap being used in the same design. Product labels, and industrial manufacturers just love pure vector design. At first I did not appreciate vector's at all until I started studying flyer design and realized how prominent vector's were in that genre design (also the ability for crisp enlargements). Adobe's Illustrator is a leading vector design and creation product; it is the industry standard and is used daily to create logo's, ads, etc.
You can use Photoshop to create vector design but Illustrator really gives you all kinds of tools for vector production. But what's really exciting is how vector and bitmap complement each other in design. After I started intensely studying design in different genres I realized this importance. As a designer you should be aware of the balance between vector and bitmap. Study it everywhere you look, from cd covers, to labels, to print advertisements, to brochures, to corporate reports, to everything!
It's everywhere...design is all around us daily in the civilized world. You cannot escape it! As graphic designer's we must be aware of the balance between vector and bitmap and how to effectively create graphic design that "sells" or effectively gets across a message. The best advice I can give you is to take the time to just "study" this balance. Look in magazines at the ad's themselves and study them.
Note how they use the text and shapes in harmony with photography. Then you can get in Photoshop and start re-creating this balance off of what you see in the everyday world of what works.
Here is a recent design...notice the balance of shapes and "photos" so prominent in product packaging (for example).
You should learn how to expand your skill as a Photoshop designer and learn how to produce these ever-present designs that heavily rely on the balance of the two image formats. Learn to understand this balance from a designer's point of view and you'll soon be seeing ad's and posters and counting the layers going through the actions you would take in Photoshop to create it.
More Photoshop: 
