Short answers, pulled from the story.
The Soviet Union became a charter member of the United Nations in 1945. Joseph Stalin initially hesitated to join the group before US president Franklin D. Roosevelt actively worked to convince him to participate.
The Soviet Union cast its veto 109 times by 1973. This accounted for most of the 128 vetoes used by the council during that period and further actions were taken by the United Nations for 75% of these vetoes.
Yakov Malik walked out of the United Nations as the sole Soviet representative in January 1950 because the Soviet Union supported the Communist government of mainland China over the Nationalist government of the Republic of China. He announced they would boycott further Security Council meetings which led to the council voting for intervention in what became the Korean War without Soviet representatives present.
Eleven Soviet republics signed the Alma-Ata Protocol on the 21st of December 1991 which established the Commonwealth of Independent States and declared the USSR ceased to exist. The protocol stated that Russia would assume Soviet UN membership including its permanent Security Council seat and Yuli Vorontsov delivered a letter from Boris Yeltsin confirming this transfer on the 24th of December 1991.