Short answers, pulled from the story.
The Free Territory of Trieste was established on the 15th of September 1947, when the peace treaty between the United Nations and Italy was ratified. It was de facto dissolved in 1954, meaning it existed for approximately seven years.
The territory was created to accommodate a mixed Italian and South Slavic population in a neutral independent country and to ease territorial rivalry between Italy and Yugoslavia. Its strategic importance for trade with Central Europe made it too valuable for either country to concede outright.
Zone A covered 222.5 square kilometers, including the port city of Trieste and a coastal strip, and was administered by British and American forces with a population of 262,406. Zone B covered 515.5 square kilometers in north-western Istria with 71,000 residents and was administered by the Yugoslav army.
The Soviet Union rejected the candidacy of twelve successive nominees for the civilian governor between October 1947 and March 1948, blocking the appointment required under UN Security Council Resolution 16. Because no governor was ever confirmed, the territory never functioned as a genuine independent state.
Following the London Memorandum signed on the 5th of October 1954, Zone A including the city of Trieste passed to Italian administration and Zone B to Yugoslavia. The border dispute between the two countries was only formally resolved with the Treaty of Osimo, signed in 1975 and ratified in 1977.
The Free Port of Trieste was a major port with customs-free status dating to 1719, a privilege confirmed in Annex VIII of the 1947 Treaty of Peace with Italy. That annex prohibited the levying of customs duties on goods imported, exported, or in transit through the port beyond charges for services rendered.