Graphic Designers need to have excellent knowledge of Typography, great research capabilities, to be creative upon demand, to be professional, meet multiple dead lines, have wonderful communication skills, make beautiful presentations, face down the competition, use iMacs, live through the cynics, be capable of illustrating the most bizarre of concepts, create memorable corporate identities and keep in touch with the latest fashions/trends just to make a living.
A lot goes into the designs, most of it unseen, so basically they're just like everyone else in most respects.
Qualified graphic designers, though it is tricky, should know how to work within space, time and cost constraints, though there is an error margin

Graphic Design subjects:

Graphic Design is in everything, a lot of designers specialise in the areas they feel most comfortable with.