what is the UN's involvment in world affairs and who governs the UN and how?

Answer 1

The following description is from Wikipedia:
"The United Nations (UN) is an international organization whose stated aims are to facilitate co-operation in international law, international security, economic development, and social equity. It was founded in 1945 at the signing of the United Nations Charter by 51 countries, replacing the League of Nations founded in 1919.
The organization's structure still reflects in some ways the circumstances of its founding, which has led to calls for reform. The five permanent members of the UN Security Council, each of which has veto power on any UN resolution, are the five main victors of World War II or their successors: People's Republic of China (which replaced the Republic of China), France, Russia (which replaced the Soviet Union), the United Kingdom, and the United States.
As of 2006, there exist 192 United Nations member states, including virtually all internationally recognized independent states. From its headquarters in New York City, the UN's member countries and specialized agencies give guidance and decide on substantive and administrative issues in regular meetings held throughout each year. The organization is divided into administrative bodies, including the General Assembly, Security Council, Economic and Social Council, Secretariat, Trusteeship Council, and the International Court of Justice (ICJ), as well as counterpart bodies dealing with the governance of all other UN system agencies, such as the World Health Organization (WHO) and United Nations Children's Fund (UNICEF)."
Follow the links below for more details and information.
[1] Wikipedia
[2] United Nations website

Answer 2

The UN is made up of different countries who work together dealing with issues that affect the world. They make up rules that all the members are suppose to follow. Hope that answer your question.