It is obvious that the "UN covers for US aggression" and Sottile provides all the historical details that illustrate this truth. However the "how" is not well explained. Permit me to fill in the "how".
The term "United Nations" was first used by President Franklin Roosevelt in early 1941 as a propaganda gimmick during a meeting with Prime Minister Winston Churchill in August of 1941 in Newfoundland, Canada. This term was officially referred to in the Atlantic Charter as a part of a more elaborate propaganda campaign waged by the leaders of the embryonic Anglo-American capitalist empire (later to become the US-led Empire) to wrap themselves in high-minded principles. (Churchill had considerable difficulty with the third principle of the Charter because of India's strong desire for independence: "all people had a right to self-determination", and he never took it seriously, nor did US officials as subsequently illustrated in Vietnam.) Such a propaganda campaign was needed in order to rally isolationist Americans to the Anglo-American cause and to enlist the support of many neutral nations in their contest with their overtly fascist competitors, the Axis powers (Germany, Italy, and Japan) for world dominance. As you can see, these two warring capitalist camps were little more than what we commonly recognize as neighborhood gangs fighting over the control of turf.
At this time only Britain and Russia were engaged in this war (WWII), but FDR was a diehard anglophile and anti-fascist capitalist, and saw the necessity of the US coming to the aid of desperate Britain. He did everything he could to support the British in spite of widespread isolationist sentiment and opposition in the US that was mostly engineered by the fascist wing of the capitalist ruling class. Both Britain and later the US were forced to ally themselves temporarily with the Soviet Union, their arch-enemy, in order to defeat their rival, the German Reich, for world dominance .
After the Allied victory in WWII, the US, which was by far the dominant power in the world as forecast by the fascist promoters of the "American Century", and its subordinate partner Britain established what was originally known as the United Nations Organization. Of course with such origins the organization was largely dominated by the US. The first indication of the latter was the UN resolutions in 1950 condemning North Korea's invasion of South Korea--although this happened after many provocations by the US-backed South Korean forces (read The Origins of the Korean War, v1 by Bruce Cumings). This was the pretext for President Harry Truman, without a declaration of war, to order troops to Korea to enforce these resolutions (in reality to contain and roll-back a communist government). In order to provide the US's intervention with more legitimacy as a UN force, the US managed to get token forces from other nations to join them.
As another indication of the US domination of the UN, despite many UN resolutions condemning Israel for their settlements on Palestinian territory, there has never been an attempt to enforce them with any military actions.