Short answers, pulled from the story.
The North Atlantic Treaty Organization began its life on the 4th of April 1949 when twelve nations signed a document in Washington. These founding members included Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States.
NATO took its first wartime action by shooting down four Bosnian Serb aircraft violating the no-fly zone on the 28th of February 1994. This occurred after NATO complied with a UN Security Council Resolution to enforce a ban starting on the 12th of April 1993 with Operation Deny Flight.
Hungary, Poland, and the Czech Republic officially joined NATO at the 1999 Washington summit while Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, and Slovenia followed in 2004. Albania and Croatia joined in 2009, Montenegro became a member in 2017, North Macedonia in 2020, Finland in 2023, and Sweden in 2024.
NATO's main headquarters are located in Brussels, Belgium while its military headquarters sit near Mons, Belgium. The civilian structure includes the North Atlantic Council which convenes at least once a week to take major decisions regarding NATO policies through consensus without voting or majority decision making.
Since 2006, the goal has been for each country to spend at least 2 percent of its gross domestic product on defense. On the 17th of June 2024, Secretary General Jens Stoltenberg announced that a record 23 of 32 member states were meeting their defense spending targets of 2 percent of GDP.