The Russian Revolution was actually a series of revolutions- two to be exact.
By 1917, most Russians had lost faith in the czarist regime. There was a lot of government corruption, and Czar Nicolas II of the Romanov family, who had ruled since 1613 with the rule of Michael I, had repeatedly dissolved the Dumas, or council assemblies created by the Emperor of Russia.
The immediate cause of the February Revolution was their involvement in WWI. Imperial Russia was no match for industrial Germany. Russian troops were ill-equipped for fighting, and Russian casualties up until that point were greater than those sustained by any nation in any previous war. Meanwhile, the Russian economy was disrupted by the costly war effort, and moderates joined Russian radical elements in calling for the overthrow of the czar.
90,000 demonstrators took to the streets on March 8th, 1917, and they clashed with police. Three days later, Nicholas formally abdicated his throne, marking the end of the Russian empire. They were replaced by the Russian Provisional Government under Prince Georgy Lvov. The Provisional Government was an alliance between the liberals and socialists who wanted political reform.
During July of that same year, there were spontaneous demonstrations against the Russian Provisional Government that lasted from July 3rd to 7th, and those were called the July Days. The military attacked the peaceful demonstration and engaged in repression against the Bolsheviks, or the Communist Party. The outcome of the July Days represented a temporary decline in the growth of the Bolsheviks. Lenin went into hiding, while the other leaders were arrested.
Finally, on July 24th, a new cabinet, formed of mostly communists, was formed with Alexander Kerensky as its head. During that time, workers began to from councils and they criticized the Russian Provisional Government. In October, the rising contempt with the provisional government reached a boiling point. In Petrograd, they had the October Revolution. They overthrew the provisional government and gave power to the soviets. The Bolshevik Party (Communist Party) was heavily supported by the soviets. After that, it created a five year civil war, which culminated in the 1922 founding of the Soviet Union.