Alexander II's Emancipation Manifesto liberated serfs in an effort to modernize Russia, but the ex-serfs had to buy land at high prices, putting them deep into debt. Due to this, most of the peasantry remained in poor and hungry.
Nicolas II does little to address the problems of the peasant class, who are suffering from famine and inflation. Furthermore, the elites are also annoyed at the large political power that Rasputin has.
I am Lenin the new ruler of Russia
Tensions boil over as the loss during the Russo Japanese War as well as losses during WWI lower public perception of the Tsar and combine with peasant unrest to form massive protests that shut down factories and farms.
In the February Revolution, the Tsar was overthrown and the Duma set up a Provisional Government that was ineffective. However, a group of radical socialists called the Bolsheviks, led by Vladimir Lenin, started to gain popularity.
In the October Revolution, the Bolsheviks overthrew the Provisional Goverment and established a new government with Lenin as its leader.
Lastly, the Russian Civil War occurs with the Red Army Bolsheviks fighting against the White Army and other parties. The Bolsheviks won in the end and formed the Soviet Union.