Short answers, pulled from the story.
The Covenant of the League of Nations was signed on the 28th of June 1919 as Part I of the Treaty of Versailles. It became effective together with the rest of the Treaty on the 10th of January 1920.
The Senate voted 49 to 35 in favor of ratification but could not reach the required two-thirds majority. Many Republicans, led by Henry Cabot Lodge of Massachusetts and Frank B. Brandegee of Connecticut, objected chiefly to Article 10, which they believed would obligate the United States to defend other nations in foreign conflicts.
Article 10 obliged League members to respect and preserve the territorial integrity and political independence of all other members against external aggression. President Wilson described it as a moral rather than a legal obligation, arguing that Congress retained authority to reject any League Council vote invoking it.
Article 16 was invoked for the first and only time during Italy's invasion and occupation of Ethiopia under Mussolini. Fifty out of 54 League members voluntarily agreed to apply sanctions, but those sanctions excluded oil and coal and failed to halt the war. The military action provisions of Article 16 were never invoked.
No great power attempted to invoke Article 16 during the Japanese invasion of Manchuria. The League Council tried to pass a resolution calling for Japan's withdrawal, but Japan vetoed it with a single negative vote. The Assembly later voted 42 to 1 to recognize Manchuria as Chinese territory, but without Article 16, the League had no means of enforcement, and Japan withdrew from the League a month later.
Article 22 placed territories formerly belonging to the Ottoman and German empires under the administration of European powers, chiefly Britain and France. The Covenant formally distinguished Mandates from colonies and sorted them into tiers based on assessed readiness for independence. South West Africa, present-day Namibia, was assigned to South Africa as a Mandate partly because of its geographical proximity.