Short answers, pulled from the story.
Bergen-Belsen was liberated on the afternoon of the 15th of April 1945, by British forces, with the first two people to reach the camp being Lieutenant John Randall of the British Special Air Service and his jeep driver, who discovered it by chance on a reconnaissance mission. British and Canadian troops found over 13,000 unburied bodies and around 60,000 inmates, most acutely sick and starving.
Current estimates put total deaths at Belsen at more than 50,000. From 1941 to 1945, almost 20,000 Soviet prisoners of war and a further 50,000 inmates died there in total. Deaths accelerated sharply in early 1945, with at least 18,168 dying in March 1945 alone, and another roughly 14,000 dying after liberation by the end of June 1945.
Bergen-Belsen began as a construction workers' camp when the Wehrmacht built a large military complex near Bergen starting in 1935. After the invasion of Poland in September 1939, the huts were repurposed as a prisoner of war camp, and from June 1941 it expanded as Stalag XI-C (311) to hold Soviet POWs. Only in April 1943 did the SS take over part of it as a concentration camp.
Yes. Margot and Anne Frank were among the women transferred to Bergen-Belsen's women's camp, which was established in August 1944. Both died there in February or March 1945, shortly before the camp was liberated on the 15th of April 1945.
The Belsen trial was held by a British military tribunal in Luneburg from September 17 to the 17th of November 1945, with 45 defendants including former commandant Josef Kramer and SS guards such as Irma Grese and Elisabeth Volkenrath. Eleven defendants were sentenced to death; the executions took place on the 13th of December 1945, in Hamelin. By June 1955, the last of those sentenced had been released after most prison terms were substantially reduced on appeal.
A redesigned memorial site opened in October 2007, including a large Documentation Centre and permanent exhibition on the grounds of the former camp. The site includes monuments to the dead, a "House of Silence" for reflection, and Jewish, Polish, Dutch, and Turkish national memorials. The Federal Government of Germany has provided ongoing funding since 2009.