Short answers, pulled from the story.
The Polish-Lithuanian Commonwealth was founded on the 1st of July 1569 with the signing of the Union of Lublin, and it ceased to exist in 1795 after being partitioned by Russia, Prussia and Austria. Poland and Lithuania were not re-established as independent countries until 1918.
Golden Liberty was the political system of the Commonwealth in which the king was elected by the nobility, bound by the Henrician Articles and a pacta conventa, and subject to veto by the Sejm parliament. A key feature was the liberum veto, which allowed any single Sejm deputy to dissolve a parliamentary session and nullify all legislation passed at it.
At its peak in the early 17th century, following the Truce of Deulino in 1618, the Commonwealth spanned approximately one million square kilometres and had a population of around twelve million people.
The Constitution of the 3rd of May 1791 was the first modern codified national constitution in European history, and the second in world history after the United States Constitution. It abolished the liberum veto, established separation of powers and extended political rights to the bourgeoisie, but was never fully implemented because neighbouring powers invaded the Commonwealth shortly after its adoption.
The Warsaw Confederation Act of 1573 guaranteed freedom of worship to all inhabitants, making the Commonwealth unusually tolerant by European standards. Roman Catholics, Jews, Orthodox Christians, Protestants and Muslims coexisted under legal protection, and by the mid-16th century eighty percent of the world's Jews lived in Poland.
The Commonwealth was weakened by the liberum veto, which foreign powers exploited by bribing individual Sejm deputies to block reforms, plunging it into political paralysis for over a century. When the 3rd of May 1791 constitution attempted serious reform, Russia, Prussia and Austria saw a strengthened Poland as a threat and partitioned the state in three stages, completing its erasure from the map by 1795.