Marxism
In the 1840s, Marx began to argue that the only way for socialism to happen was for workers themselves to force the change. He wrote of a society where the workers owned the factories and farms where they were employed. Other elements of a Marxist society included free education, the abolishment of the army of the prior state, the right to vote and the right to determine representatives' pay and recall them if necessary. Marx's ideas greatly influenced Vladimir Lenin, one of the leaders of the Russian Revolution.
Stalinism
After Lenin's death, Stalin led the Soviet Union from 1929 to 1953. Although he claimed to be putting the ideas of Marx and Lenin into practice, he formed a dictatorship where he held all the power. He set aside Marx's aim of the necessity of a worldwide revolution of workers and instead said that a communist Russia could exist surrounded by a capitalist world. To make Russia strong, he nationalized the farms and spent large sums on developing industry. Stalinism exacted a terrible toll on the people of Russia. Estimates of deaths range as high as 20 million.
Misconceptions
Perhaps the biggest misconception about Marxism and Stalinism is that they are more or less the same thing. This could not be further from the truth. While Marx hoped to elevate the status of workers, Stalin repressed workers because he believed it was necessary for the good of the state. Also, you might have heard that these political and economic systems suppress the individual. While Stalin certainly did this, Marx believed socialism, then communism, are the best ways to achieve democracy for everyone.

Marxism-Leninism is (very simply) the belief that the state should own all the means of production, that the workers should be led by a "vanguard "party (a party of intellectuals who understand the proletariat's class-consciousness"), that the workers and peasants are the revolutionary classes, and, most importantly, that Marx's "historical phases of history" can be shortened - "telescoped" as Lenin put it.

Stalinism is the addition to these several political and economic features:
1) Marxism-Leninism is an internationalist ideology, it believes that the communist revolution is inevitable, and once it has happened in one country, then others will soon have their own revolutions - and so it was their duty to try to export the revolution.Stalin disagreed, he wanted to consolidate the revolution, so he began the policy of "Socialism in One Country".
2) Stalinist economics called for the farms to be amalgamated into collective farms and the farmers to become agrarian workers. It also calls for all economic activity to be owned and controlled by the state through a centrally devised Five Year Plans worked out through the state planning agency - Gosplan. The state's industrial focus became heavy industry - mining, iron and steel production and ship building.
3) Another feature that marks Stalinism out from other kinds of socialism and communism is the gross