The purpose of accrediting a college is to ensure that the institution or program meets certain educational requirements. Mentioning a college's accreditation is a large part of its promotional campaign. Checking to see that a person has a degree from an accredited, rather than an uncredited, college is a standard step in evaluating a job applicant's credentials and education as they relate to a job description.
In most countries, accreditation happens through their governments' educational agencies. Common checklists for accrediting a school include examining the overall mission and objective of the school and assessing student requirements for admissions.
In the United States, accreditation does not happen through a government agency. It is done through private accreditation bodies endorsed by the U.S. Department of Education and the Council for Higher Education Accreditation (CHEA.) The secretary of education releases an annual list of approved accreditation agencies, that publish their own list of accredited schools.
Schools can also receive programmatic accreditation, recognition in a specific subject area such as medicine, construction education, pastoral education, business or computer science. These specialized evaluations are done through agencies like the National Architectural Accrediting Board or the American Library Association.