Short answers, pulled from the story.
The French Union was a political entity established by the French constitution of the 27th of October 1946, extending the French Fourth Republic to former colonies. It replaced the formal designation of French colonies with a single framework that grouped metropolitan France, overseas departments, overseas territories, associated states, and UN Trust Territories as one entity.
The French Union comprised metropolitan France (including Corsica and French Algeria), old colonies that became overseas departments in 1946 such as Guadeloupe and Martinique, new overseas territories such as Senegal and Madagascar, associated states including the kingdoms of Cambodia and Laos and the State of Vietnam, and United Nations Trust Territories such as French Cameroons and French Togoland.
The French Union was dissolved in 1958 following the fall of the French Fourth Republic. It was replaced by the French Community under Charles de Gaulle's Fifth Republic, following a constitutional referendum held on the 28th of September 1958.
Guinea's leading political activists preferred immediate and complete independence rather than joining the French Community. More than 95% of Guinea's voters rejected the new constitution in the referendum, with a turnout of 85.5%. In response, French officials destroyed furniture, lightbulbs, windows, and other equipment before departing, and over 3,000 French civil servants and army health officials left the country.
Felix Houphouet-Boigny and Leopold Senghor were among the most prominent African supporters. Houphouet-Boigny pointed to the over 600 billion Francs disbursed to French colonies through the Central Fund for France Overseas and to new democratic freedoms such as elected territorial assemblies. Senghor, after visiting Cote d'Ivoire in 1952, believed Franco-African cooperation was mutually beneficial and argued for greater economic and political integration rather than separate national development.
All three withdrew in 1954-1957. Vietnam withdrew on the 20th of July 1954 and terminated its economic and financial agreements with France in December 1955. Cambodia withdrew on the 25th of September 1955. Laos withdrew on the 11th of May 1957 by amending its constitution.