Short answers, pulled from the story.
The conflict began when Russian troops crossed the River Prut into Moldavia and Wallachia in July 1853 under a pretext of protecting Orthodox Christians. Tsar Nicholas I expected European powers would not object to annexing neighboring provinces, but Britain could not tolerate Russian dominance of Ottoman affairs.
The Battle of Sinop occurred on the 30th of November 1853 when a Russian squadron destroyed an Ottoman patrol force of 11 warships anchored in port. This naval engagement became known as the massacre of Sinope and served as propaganda for Western public opinion.
Admiral Pavel Nakhimov fell during fighting on the 30th of June 1855 while Lord Raglan died on the 28th of June. The siege lasted 337 days until the city fell on the 9th of September 1855 after French capture of the Malakoff fort.
Fewer than half of the 80,000 Russian soldiers who crossed the Prut River survived due to sickness rather than combat action. Medical services ranged from bad to nonexistent within the Russian Army causing widespread death from disease.
These failures became catalyst for reforms including emancipation reform of 1861 abolishing serfdom across Russian territories. Overhauls followed in justice system local self-government education military service addressing root causes exposed by battlefield defeats.