Short answers, pulled from the story.
The Battle of Chancellorsville was fought from the 30th of April to the 6th of May, 1863, during the American Civil War. The broader Chancellorsville campaign ended on the 7th of May when Union cavalry withdrew into lines east of Richmond.
Stonewall Jackson was struck by friendly fire on the night of the 2nd of May 1863, when men of the 18th North Carolina Infantry mistook his returning reconnaissance party for Union cavalry and opened fire. Three bullets hit him, his left arm had to be amputated, and he died of pneumonia on the 10th of May, eight days after being shot.
Some historians describe Chancellorsville as Lee's "perfect battle" because he defeated a Union force more than twice the size of his own by dividing his outnumbered army twice in the face of the enemy, achieving a decisive Confederate victory through aggressive maneuvering. Despite being outnumbered by a ratio of more than two to one, Lee inflicted a significant defeat on Hooker's Army of the Potomac.
Lee's Army of Northern Virginia suffered 13,303 casualties from roughly 60,000 men engaged, about 22% of his force. The Union Army of the Potomac, with approximately 133,000 men engaged, lost 17,197 casualties. The fighting on May 3 alone produced 21,357 combined casualties, making it the second bloodiest single day of the Civil War after Antietam.
Maj. Gen. Oliver O. Howard commanded the XI Corps, whose right flank was routed by Jackson's surprise attack on May 2. Howard failed to prepare defenses against an attack from the west despite direct orders from Hooker, ignored multiple warnings from subordinates including Col. Leopold von Gilsa and Capt. Hubert Dilger, and left only two cannons positioned to cover an exposed flank. He partially redeemed himself through personal bravery during the rout, rallying troops while waving a flag under the stump of his amputated arm.
Hooker lost through a combination of his own timid decision-making, poor subordinate performance, and bad luck. He halted a promising offensive advance on May 1 and ordered Sickles to abandon the critical high ground at Hazel Grove on May 3. He was struck by a cannonball at 9:15 a.m. on May 3 and was likely concussed, yet refused to turn command over to Darius Couch. He also left roughly 40,000 of his men scarcely engaged throughout the battle.