Think of the logos that need no words but are immediately recognizable -- the Nike swoosh, Apple's apple, the NBC peacock. All were the work of graphic designers skilled in corporate identity and branding.
Graphic designers who work in branding help a company project a desired image. To do this, they research the industry and the customers (the target audience), and then use skills in logo design, letterhead design, typeface design, packaging, and copywriting to create images and graphics that will inspire the customer to take action.
The goal of a company brand is to be easily identifiable, unique, and desirable. And over time, if successful, the brand may come to be a household name, immediately identifiable by a simple shape or text.