The correct answer is "true."
If you mean that the Soviet Union participated in the negotiations and agreements to create the United Nations in 1945, then yes, the correct answer is true.
Indeed, the Soviet Union had an active participation with the creation of the UN and was part of the Security Council of the United Nations.
However, major differences between the USSR and the United States and Great Britain made the USSR keep its distance from western European countries and the United States. The Cold War had begun.
The western European countries founded NATO with the United States, the North Atlantic Treaty Organization. On the other hand, the Soviet Union signed the Warsaw Pact with the Eastern European countries such as Czechoslovakia, Poland, Hungary, Romania, and East Germany.