Short answers, pulled from the story.
The OSCE traces its origins to the Conference on Security and Co-operation in Europe (CSCE), which opened in Helsinki on the 3rd of July 1973 with 35 states. It was renamed the OSCE on the 1st of January 1995, following decisions taken at a Budapest conference in 1994.
The Helsinki Final Act is the founding document signed by 35 states at Finlandia Hall between the 30th of July and the 1st of August 1975. It is not a binding treaty but a political commitment; for the first time, signatories accepted that a government's treatment of its own citizens is a legitimate matter of international concern.
The OSCE has 57 participating countries, mostly in Europe but with some members in Asia and North America. Together they cover approximately 55.4% of the land area of the Northern Hemisphere.
The OSCE deployed the Special Monitoring Mission to Ukraine on the 21st of March 2014 at Ukraine's request to observe the conflict in Donbas. The mission monitored ceasefires, deployed drones to watch borders, and produced field reports until its mandate expired on the 31st of March 2022 when Russia declined to renew it.
The Office for Democratic Institutions and Human Rights (ODIHR), based in Warsaw, has observed more than 300 elections and referendums since 1995, sending more than 50,000 observers. Between 1994 and 2004 alone it monitored more than 150 elections, and in 2004 it observed the U.S. presidential election for the first time.
The OSCE operates by consensus, meaning any single participating state can veto decisions on budgets, events, or mission extensions. Russia and Belarus have exploited this rule to block the appointment of Estonia as chair for 2024 and to limit the Moldova mission mandate to six-month renewals rather than annual ones.