Short answers, pulled from the story.
NATO has 32 member states. Thirty are in Europe and two, Canada and the United States, are in North America. Sweden's accession on the 7th of March 2024 brought the alliance's total combined territory to 27,580,492 square kilometres.
NATO was founded on the 4th of April 1949 with the signing of the North Atlantic Treaty. The 12 founding members were Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States.
Article 5 states that an armed attack against one member is considered an attack against all, and other members shall assist, with armed forces if necessary. Article 6 limits this guarantee geographically to the North American and European mainlands, the islands north of the Tropic of Cancer, and the entirety of Turkey, meaning places like Hawaii, Puerto Rico, and the Falkland Islands are excluded.
Three NATO members are nuclear-weapons states: France, the United Kingdom, and the United States. France is the only member outside the Nuclear Planning Group and unlike the US and UK will not commit its nuclear-armed submarines to the alliance.
Iceland is the only NATO member without a conventional army. It maintains a coast guard and a small unit of civilian specialists designated for NATO operations.
NATO added 16 members between 1999 and 2024. The Czech Republic, Hungary, and Poland joined in 1999; seven more Eastern European nations joined in 2004; Albania and Croatia in 2009; Montenegro in 2017; North Macedonia in 2020; Finland in 2023; and Sweden in 2024. All except Finland and Sweden were formerly part of the Warsaw Pact or the former Yugoslavia.