Marxism–Leninism was practiced by the Soviet Union (USSR) after the Bolshevik Revolution. It was also practiced by the Stalinists in the USSR.
The purpose of Marxism–Leninism is to turn a capitalist state into a socialist state. This is done by a revolution by the proletariat to overthrow the old government. The new government then creates a "dictatorship of the proletariat". This new government leads the country based on democratic centralism.