Wikipedia has a nice entry on the subject; strategy, tactics, statistics, logistics... I'll just say it was a battle marked by completely incompetent leadership and staggering losses. Great masses of human beings, Frenchmen and Germans in the hundreds of thousands, mangled and obliterated by constant artillery fire. Huge guns. Mud and blood, the screams of the dying, and incessant, ear-splitting explosions. Hell on earth. For 303 days, from February 21st to December 18th, 1916. Many went crazy.
So who won? The Germans withdrew and so the French declared victory, but they lost so many men that it was a Pyrrhic victory, if ever there was one. The French army was so badly weakened, in fact, that it was near collapse until the U.S. entered the war in 1917 and picked up the slack.
"Humanity is mad. It must be mad to do what it is doing. What a massacre! What scenes of horror and carnage! I cannot find words to translate my impressions. Hell itself cannot be so terrible. Men are mad!"
-- Lt. Alfred Joubaire, 1916
(killed soon thereafter by an artillery shell)