Everything about the United Nations is working towards World Peace. While this is not always possible, countries can take advantage of their services to ensure the smooth running of their country and smooth negotiations with other countries.
From laying down the law to ensuring a countries security and from economic development to human rights, the United Nations have a lot of duties on their hands as they work to world peace.
They basically manage the world. This is the easiest way to explain it. They govern the law, they help suffering countries and they lay down the law when it comes to human rights. They are the governing body of the world. With their court system for international law and their security teams, they are able to ensure the everything around the world runs as smoothly as possible, making it a better place to live.