Short answers, pulled from the story.
Operation Wilfred was a British and French naval operation carried out on the 8th of April 1940. It involved laying mines in the channels between Norway and its offshore islands to stop Swedish iron ore from being shipped through neutral Norwegian waters to Germany.
Germany received approximately 20 million long tons of Swedish iron ore in 1938, and the Allied blockade had denied roughly 9 million long tons since 1939. The Norwegian Leads, a protected coastal corridor, allowed German ore ships to travel safely. Mining those waters was intended to close that route and damage Germany's war economy.
Plan R4 was the Allied contingency plan prepared alongside Operation Wilfred. The British anticipated that mining Norwegian waters would provoke a German response, and Plan R4 called for occupying Stavanger, Bergen, Trondheim and Narvik to forestall German landings as soon as Germany revealed its intentions.
HMS Glowworm, under Lieutenant-Commander Gerard Roope, became separated from the main force on the 7th of April 1940 while searching for a man overboard. She encountered the German heavy cruiser Admiral Hipper, attacked with torpedoes, and after taking severe damage rammed the cruiser before sinking. 111 men were lost and Roope received a posthumous Victoria Cross.
Operation Wilfred failed to cut off iron ore shipments to Germany. The mining was overtaken by Germany's Operation Weserübung, the invasion of Norway and Denmark that began on the 9th of April 1940. Norway surrendered on the 9th of June 1940, and the iron ore route was never effectively severed.
The Altmark incident took place on the 16th and the 17th of February 1940, when British ships entered Norwegian territorial waters to rescue merchant sailors held aboard the German vessel Altmark. The episode demonstrated to Churchill that limited operations in the Norwegian Leads were feasible, and on the 20th of February he ordered the Admiralty to urgently prepare the minelaying plan that became Operation Wilfred.