How to join the United Nations?

Nick is correct. You should begin with a university education. There is a little known trick to "backdooring" your way into a UN job. However, it takes a bit of sacrifice for a couple of years. Just as the United States government recruits college educated people to join the US Peace Corps and serve overseas for 2 years (which BTW opens doors to US government civil service careers since you are already technically a civil servant as a Peace Corps volunteer) The United Nations also has a Peace Corps. the two organizations are almost identical in what they do and how they operate. As a UN Peace Corps volunteer you will serve overseas in a country doing "community building" for lack of a better term. You will be paid the equivalent of the average family of 4 in whatever country you are stationed in. You will also live in the same housing as the everyone else in that community, sometimes in rented housing that the Peace Corps have arranged for you. In 2 years your tour will end and you return to the states but you are already employed by the UN as a regular employee and open positions in the UN will go to "internal transfer hires" before they go to outsiders who are not already employed by the UN. In short, you will get first crack at any open positions. One might question, as I do, why you are even interested in the UN as an organization though. They are not well respected. In fact, at best, they are regarded as a "straw man" organization that is overly bureaucratic, with no authority at all as an organization and virtually no nation actually (truly) cares what the UN's opinion or position is on anything. They are virtually ignored by most countries.