The United Nations were created on October 24 of 1945 in the aftermath of WWII. They were created to maintain international peace and foster international cooperation and friendly relations between nations of the world. Currently 193 countries of Earth are members.
The five countries that were given permanent seats are: China, France, Russia, the United Kingdom, and the United States. The reason why their seats are permanent is that it was agreed upon during the creation of the UN in 1945. The reason was that these five nations were the victors against the Axis after WWII and were considered as responsible for international security due to their powerful armed forces.