Short answers, pulled from the story.
The main French forces entered the city on the 17th of August 1812 after Polish troops breached the walls. The battle concluded with Barclay de Tolly retaining forces until the night of the 18th of August to cover his retreat.
General Michael Andreas Barclay de Tolly commanded the First Western Army at the start of the engagement. He was replaced by General Mikhail Kutuzov on the 29th of August following a crisis in the Russian high command.
Of the 2,250 buildings in the historic fortress city, 84% were destroyed leaving only 350 intact. The intense artillery bombardment set the city on fire and resulted in vast destruction of the urban area.
Estimates for Russian casualties range from 6,000 to 14,000 men according to historians like David Chandler and Alexander Mikaberidze. Docturov's VI Corps alone suffered 10,800 casualties reducing its strength from 16,800 to 6,000 combat-capable soldiers.
Napoleon ordered a general assault with three corps supported by two hundred artillery pieces to capture the fortified city defended by Bagration's troops. He intended to cut off the Russians from Moscow and destroy the isolated Russian army through this operation.