Short answers, pulled from the story.
Vatican City was officially established as an independent state on the 11th of February 1929 when the Lateran Treaty was signed between the Holy See and the Kingdom of Italy. The treaty was ratified and took effect on the 7th of June 1929, creating the Vatican City State to provide the Holy See with temporal jurisdiction and independence.
The Vatican City State was created by the Lateran Treaty signed on the 11th of February 1929 by Prime Minister Benito Mussolini on behalf of King Victor Emmanuel III and Cardinal Secretary of State Pietro Gasparri for Pope Pius XI. This agreement resolved the Roman Question and established the independent state of Vatican City distinct from the Holy See.
Vatican City has a population of 882 residents regardless of citizenship, with citizenship granted on jus officii based on appointment to work in a certain capacity in the service of the Holy See. This includes Cardinals, diplomats, and other employees, and citizenship usually ceases upon the cessation of the appointment.
Popes began living at the Vatican permanently in 1870 after the capture of Rome and the annexation of the Papal States by Italian forces. They had previously resided at the Lateran Palace for about a thousand years and lived in Avignon from 1309 to 1377 before returning to Rome.
Vatican City has used the Euro as its currency since January 1999 following a special agreement with the European Union. Euro coins and notes were introduced on the 1st of January 2002, and the Vatican City does not issue euro banknotes.
Vatican City was added to the List of World Heritage Sites by UNESCO in 1984 as the only site to consist of an entire state. It is also the only UNESCO site registered as a centre containing monuments in the International Register of Cultural Property under Special Protection according to the 1954 Hague Convention.