The October Revolution took place throughout the Autumn of 1917 and ended up with Lenin and the Bolsheviks seizing power from the Provisional Government.
After the abdication of the tsar, the Provisional Government was formed to rule over what used to be the Russian Empire. However, in parallel to them, there was also the Soviet, which was a sort of council formed of all the left-wing political parties including the Bolsheviks (Communists) and the Socialist Revolutionaries. The Soviet held less power than the Provisional Government and was elected by the people. For many months after the abdication, the Soviet was mostly formed up of Socialist Revolutionaries, with the Bolshevik party holding a minority position. However by July 1917, the people were becoming more and more disapproving of the Provisional Government, largely because the class for peace, bread, and land were not being achieved, and started electing more and more Bolsheviks into the Soviet. In parallel to this timeline, Lenin was becoming more and more convinced that the Provisional Government was simply upholding the remnants of imperialism, and that it would never rule on behalf of the working class. In July 1917, Lenin was exiled from Russia on accusations of being a German Spy.
By October 1917, Lenin felt that it was finally time to rise up and seize power and so, on the 20th of October, he snuck back into St Petersburg and on the 23rd he attended a meeting of the Bolshevik Council. After a long debate, he convinced them that it was necessary to rise up, and they promptly began training all the people they could for an assault on the government. In the beginning of November (between the 7th and 8th) Lenin, the Bolsheviks, and their guards snuck into the government and forcibly took control. They announced that the power of state had been handed over to the Soviet and the Soviet, which at this point was mostly made up of Bolsheviks, happily accepted and elected Lenin as the chairman and leader.
While the short-term transition of power seemed easy, it was difficult for Lenin to consolidate this power as he faced opposition from the Allies, other foreign countries that would not recognise his government, and from opposing political parties within Russia including former tsarists and alienated socialist revolutionaries. This all cumulated in the outbreak of a Civil War which lasted from 1918 till 1920.