Short answers, pulled from the story.
The fire of Moscow 1812 started on the 14th of September 1812 and ended on the 21st of September 1812. The flames persisted for seven days while consuming three-quarters of the city's wooden structures.
Count Fyodor Rostopchin reportedly ordered the head of police to set fire to the Kremlin and major public buildings before leaving the city. General Mikhail Kutuzov utilized this scorched earth policy to weaken Napoleon's Grande Armée through attrition warfare.
Between 6,200 and 10,000 civilians chose to remain in Moscow after the French arrival alongside thousands of wounded soldiers. Most churches and monasteries survived because they were built of stone rather than wood.
Rebuilding the city under military governor Alexander Tormasov lasted well over a decade starting in 1814. Dmitry Golitsyn continued reconstruction work from 1820 until approximately 1840 to transform the devastated capital back into a functioning imperial center.
Leo Tolstoy described the occupation and fire extensively in his novel War and Peace during Book XI. Louise Fusil witnessed the event and detailed her retreat in published memoirs after living six years in Russia.