Short answers, pulled from the story.
Democratic Federal Yugoslavia was established de facto on the 29th of November 1943 through the Second Session of the Anti-Fascist Council for the National Liberation of Yugoslavia (AVNOJ) in Jajce. It was recognized by the Allied powers at the Tehran Conference.
Democratic Federal Yugoslavia was governed throughout its existence by Marshal Josip Broz Tito as prime minister. Tito was also general secretary of the Communist Party of Yugoslavia, which held 22 minister positions in the provisional government.
The Treaty of Vis, signed on the 16th of June 1944 between Tito and Ivan Šubašić, prime minister of the Yugoslav government-in-exile, obligated both governments to merge into a single provisional administration. It represented the exiled royal government's de iure recognition of the AVNOJ authority.
Democratic Federal Yugoslavia consisted of six federal states: Serbia, Croatia, Bosnia and Herzegovina, Slovenia, Montenegro, and Democratic Federal Macedonia. It also included two autonomous units, the Autonomous Province of Vojvodina and the Kosovo and Metohija Autonomous Region, both within Serbia.
The Federal People's Republic of Yugoslavia was proclaimed on the 29th of November 1945, exactly two years after the founding AVNOJ session in Jajce. The change followed the deposition of King Peter II and ended the intentional ambiguity about whether the state would be a monarchy or a republic.
Yes. Democratic Federal Yugoslavia signed the United Nations Charter in October 1945, making it one of the founding members of the UN. The state joined before formally completing its transition into the Federal People's Republic of Yugoslavia.