The best resource for finding the address of corporation's headquarters is to visit the website of the corporation in question. Typically, the website will have a "Contact" or "About" section with the corporate headquarters address listed. In addition, most products have 1-800 numbers where corporate information can be obtained.
The headquarters of a corporation are where the company's executive officers and their support staff work. Many larger corporations have their headquarters in major cities where there are more business opportunities. The majority of a corporation's employees may not work at the headquarters, but typically the headquarters is where most of the corporate decisions are made.