What changed after the October revolution?

Strictly speaking, the events of October 1917 constituted an insurrection rather than a revolution. Since February, Russia had been ruled by a dual power arrangement consisting of a predominantly liberal Provisional Government, and the Soviets, revolutionary councils representing groups such as workers, peasants and soldiers.
Most of those within the Russian political system were committed to the establishment of a Constituent Assembly, which was set to provide the country with its first ever democratically-elected government. However, the Bolsheviks, under the leadership of Lenin, had other ideas. When the results of the Constituent Assembly elections came in, the Bolsheviks found that they had finished in second place behind the Socialist Revolutionaries (SRs).
Initially, the Bolsheviks had supported the Constituent Assembly, but their position changed over the course of 1917. They became increasingly radical, calling for all power to be given to the Soviets, where they had majority support. If this were to happen, then the Constituent Assembly, and the "bourgeois democracy" it represented, would effectively be superfluous. After the Assembly convened, it lasted for all of thirteen hours before it was formally dissolved at gunpoint by troops loyal to the Bolsheviks.
In the aftermath of the forced dissolution of the Constituent Assembly, power was formally transferred to the All-Russia Congress of Soviets. In fact, however, power gradually became concentrated in the hands of the Council of People's Commissars, or Sovnarkom, headed by Lenin, and consisting of a coalition of Bolsheviks and Left SRs. Over time, Sovnarkom became the most powerful organ of executive power in Russia. Gradually, the Left SRs were eased out of government as the Bolsheviks turned Russia into a one-party state.
After the October insurrection, the Russian system of government became more repressive, and the Bolsheviks under Lenin unleashed a campaign of terror against anyone perceived to be a threat to the regime. The extensive program of civil rights enacted after the February Revolution was systematically dismantled as the Bolsheviks consolidated their dictatorship. The growing centralization of power, combined with heightened repression, set the tone for Russia's subsequent political, social and economic development until the Soviet Union's collapse in 1991.