Short answers, pulled from the story.
The League of Nations held its first council meeting on the 16th of January 1920 and formally dissolved on the 18th of April 1946. The Covenant came into force on the 10th of January 1920 following the signing of the Treaty of Versailles on the 28th of June 1919.
Lord Robert Cecil and Jan Smuts served as the two principal drafters who created the Covenant of the League of Nations. Woodrow Wilson also contributed significantly through his Fourteen Points released in January 1918 which influenced the final structure.
United States Senate Republicans led by Henry Cabot Lodge refused to ratify the treaty because they demanded reservations that President Wilson would not accept. The Senate voted against ratification on the 19th of March 1920 with a result of 49-35 falling short of the required two-thirds majority.
The Fridtjof Nansen Commission Refugees established on the 27th of June 1921 helped 425,000 ex-prisoners return home and introduced the Nansen passport for stateless people. The Slavery Commission successfully pressured governments including Afghanistan Iraq Nepal and Ethiopia to abolish slavery or forced labour between 1923 and 1942.
The League reached its maximum size of 58 members between the 28th of September 1934 and the 23rd of February 1935. This peak occurred after the Soviet Union joined in 1934 before Japan Germany and Italy withdrew during the 1930s.