Check out this YouTube Video created by the History Channel about Labor Day.

In case you did not know WHY the United States celebrates, this video will answer many of your questions.

Labor Day Timeline (an excerpt)

Like many holiday’s Labor Day’s origins and first observances are uncertain. It is widely believed that the concept for Labor Day as a recognized holiday may have been conceived independently by two individuals, both working in the same city with the possibility that the paths of both had crossed in the planning and development of Labor Day.
1870 Matthew Maguire organized his first labor union rally in 1870.
1872 Peter J. McGuire would join 10,000 New York workers marching to demand better working conditions. That would inspire his involvement in union organization.
1882 The Central Labor Union adopted a Labor Day proposal appointing a committee for the planning of a demonstration and picnic. Mathew Maguire was made the chairman of the committee.
In New York City, N.Y. a Labor Day celebration was held on a Tuesday, September 5, 1882 by the Central Labor Union.
1892 Workers in New York City took an unpaid day off to march in Union Square to support a Labor Day holiday.
1894 The U.S. Congress passed the Labor Day act on June 28th establishing the first Monday in September a legal holiday in the U.S. Territories and the District of Columbia.
Labor Day is celebrated by most Americans as the symbolic end of the summer.
Happy Labor Day from the Editors and Staff of WE Magazine for Women!