Short answers, pulled from the story.
The Battle of Kursk is the single largest battle in the history of warfare. It was also the deadliest armoured battle, the largest tank battle, and its opening day on the 5th of July 1943 was the costliest single day in aerial warfare by aircraft shot down. It was the last strategic offensive Germany launched on the Eastern Front.
The Soviets learned of the German plan through the Lucy spy ring in Switzerland. They verified the intelligence through John Cairncross, a Soviet spy at the Government Code and Cypher School at Bletchley Park, who forwarded raw decrypts directly to Moscow. Soviet politician Anastas Mikoyan recorded that Stalin notified him of the expected attack on the 27th of March 1943.
The Voronezh Front dug 4,200 kilometres of trenches and the Central Front dug 5,000 kilometres. Combat engineers laid 503,993 anti-tank mines and 439,348 anti-personnel mines. The total defensive depth, including fallback positions and the Steppe Front's reserves, reached nearly 300 kilometres, built with the labour of over 300,000 civilians.
The Battle of Prokhorovka on the 12th of July 1943 was a large armoured clash on the southern face of the Kursk salient, triggered when the Soviets committed the 5th Guards Tank Army to block the advance of the II SS Panzer Corps. It is recognised as the largest single armoured engagement of the battle and of the war.
Hitler cancelled Citadel after just over a week of fighting, in part because the Allied invasion of Sicily on the 10th of July 1943 forced him to divert troops from France to the Mediterranean rather than using them as a strategic reserve in the east. Heavy German losses in men and tanks also made continuing the offensive untenable.
Germany committed around 777,000 men, 2,451 tanks and assault guns, and 7,417 guns and mortars, representing about 70 percent of its armour on the Eastern Front. The Soviet force including the Steppe Front reserve totalled more than 1,900,000 men, with 4,869 tanks and 259 self-propelled guns in the Central and Voronezh Fronts alone.