Short answers, pulled from the story.
The three Partitions of Poland took place in 1772, 1793, and 1795. The First Partition was decided on the 5th of August 1772, the Second was formalized at the Grodno Sejm on the 23rd of January 1793, and the Third was signed on the 24th of October 1795.
The Habsburg monarchy, the Kingdom of Prussia, and the Russian Empire carried out all three partitions. Austria did not participate in the Second Partition of 1793, which was divided solely between Russia and Prussia.
Russia gained approximately 463,200 square kilometers across all three partitions, or about 63% of the total annexed Commonwealth territory. After the Congress of Vienna in 1815, Russia controlled 82% of the pre-1772 Commonwealth's territory, including its puppet state of Congress Poland.
A combination of internal weakness and external aggression caused the partitions. The liberum veto, which allowed any single member of parliament to nullify legislation, paralyzed the Polish government and invited foreign manipulation. Prussia, Austria, and Russia signed a secret agreement in 1730 to keep Commonwealth laws unchanged, and then used military force and political pressure to dismember it when reform threatened their influence.
Poland ceased to exist as a sovereign state for 123 years, from the Third Partition in 1795 until the Treaty of Versailles allowed the restoration of full Polish independence after World War I.
The term Fourth Partition of Poland refers to several possible subsequent annexations of Polish lands. The most common usages include the 1815 division of the Duchy of Warsaw at the Congress of Vienna and the 1939 division of Poland between Nazi Germany and the Soviet Union under the Molotov-Ribbentrop Pact. The term was also applied to the Polish diaspora, known as Polonia, whose communities sustained the project of Polish independence across generations.