Some P.R. people work for celebrities and the entertainment industry; many more work as public relations specialists in 'regular' companies. The "nature of the work" is described below from the Department of Labor's Occupational Outlook Handbook. The whole article provides much more information about the profession, such as salary ranges, educational requirements, career outlook, and more. See the whole article at: http://www.bls.gov/oco/ocos086.htm
Public relations specialists handle organizational functions such as media, community, consumer, industry, and governmental relations; political campaigns; interest-group representation; conflict mediation; and employee and investor relations. They do more than “tell the organization’s story.” They must understand the attitudes and concerns of community, consumer, employee, and public interest groups and establish and maintain cooperative relationships with them and with representatives from print and broadcast journalism.
Public relations specialists draft press releases and contact people in the media who might print or broadcast their material. Many radio or television special reports, newspaper stories, and magazine articles start at the desks of public relations specialists. Sometimes the subject is an organization and its policies toward its employees or its role in the community. Often the subject is a public issue, such as health, energy, or the environment, and what an organization does to advance that issue.
Public relations specialists also arrange and conduct programs to keep up contact between organization representatives and the public. For example, they set up speaking engagements and often prepare speeches for company officials. These media specialists represent employers at community projects; make film, slide, or other visual presentations at meetings and school assemblies; and plan conventions. In addition, they are responsible for preparing annual reports and writing proposals for various projects.
In government, public relations specialists—who may be called press secretaries, information officers, public affairs specialists, or communication specialists—keep the public informed about the activities of agencies and officials. For example, public affairs specialists in the U.S. Department of State keep the public informed of travel advisories and of U.S. positions on foreign issues. A press secretary for a member of Congress keeps constituents aware of the representative’s accomplishments.
In large organizations, the key public relations executive, who often is a vice president, may develop overall plans and policies with other executives. In addition, public relations departments employ public relations specialists to write, research, prepare materials, maintain contacts, and respond to inquiries.
People who handle publicity for an individual or who direct public relations for a small organization may deal with all aspects of the job. They contact people, plan and research, and prepare materials for distribution. They also may handle advertising or sales promotion work to support marketing efforts.