Copywriting is the act of writing copy for the purpose of selling or marketing a product, business, or idea. The term copywriting is often used interchangeably with content writing or freelance writing, though this is technically incorrect. A copywriter is one who writes for promotional purposes, and although they may very well be a freelance writer, they have a specific marketing purpose.
A copywriter might write advertising copy, sales copy, sales letters, commercial scripts, or other types of marketing media for a business, such as brochures, billboards, or mass mailings. Copywriters often write copy for commercial websites as well, often for the purpose of search engine optimization, or SEO. SEO uses frequently used search terms in the written copy to promote the ranking of the website in search engines, making it more likely for people to click on the link and visit the website. These are simply common places to find copywriting, but it can literally be found anywhere in day to day life, and you probably don't even notice it sometimes.
Journalists, reporters and other content writers are not copywriters, though they may have started out that way. Copywriting is a great way to break into the publishing industry, and a college degree in marketing, journalism, English, or some other form of writing or communications is a good way to begin. You might be able to get an internship as a copywriter while still in college, making contacts at a company and learning the basics.
Copywriting for a company is often a freelance endeavor. Though companies do certainly hire staff copywriters, it is not as likely as having a pool of available freelancers to choose from. For this reason, a copywriter might do freelance writing for a number of different companies, which can be a great way to build a resume and to make more contacts in the industry. Some copywriters are able to work from home.
Within a company, newspaper or magazine, a copywriter will probably work on a creative team within the advertising department. Because a copywriter is generally only responsible for the written word of an advertisement, she might work with an artist or a graphic designer if they are working on a print ad. If the promotional material requires only written copy, the copywriter will be able to work alone. A copywriter needs to be a creative thinker and a concise and professional writer, able to communicate ideas clearly but in a catchy, memorable way.