Agencies: The most common route into the public relations field is to join a public relations firm. Firms pitch their communication services to clients ranging from corporations to nonprofit organizations to government agencies. These services include organizing press events, writing press releases, launching new products, publishing, providing "damage control" for corporate missteps or miscommunication, as well as a variety of other strategic support.
Corporate Communications: Also referred to as the "client side" in the public relations world. There are two primary corporate communications roles, media relations and investor relations. Media relations focuses on relationships with media outlets like newspapers and television stations. Investor relations focuses on those shareholders with a financial stake or interest in the company, like stockholders, financial analysts and potential investors. Some senior executives in this field develop and maintain the overall corporate communications strategy.
Publicists: A public relations function in which the communications needs of a single individual, such as an author or other celebrity, is served. Referred to as press secretaries in politics. Publicists manage all relations with the media, promote their client's activities (or downplay them in some cases) and manage their public schedule.
Take a look at the major career paths in PR.