As this question seems a bit closer to political theory than history may I suggest you post this to /r/AskSocialscience.

To provide a very brief answer not too tied down in specifics...

The main difference in practical historical usage is one of teleological ordering. Traditional marxist theory stipulated that societies progressed through different progressions of organising themselves in relation to the social and economic relations. Classical slavery based societies would become feudal societies, which would then become capitalist societies and so on. Orthodox marxism believes essentially that imperialist capitalism will not immediately become a communist state, and that this process will take several incremental steps. In contrast, Lenin with his cadre of Bolshevik revolutionaries operated under a slightly different model. Firstly, they believed revolution could occur with societies less far along the teleology of development via a two stage revolutionary process, wherein a guided capitalist period would be used to usher in entering the socialist stage.

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So in short, Marxists believed revolution would occur in a highly developed capitalist nation, i.e. Germany or Britain, whereas Marxist-Leninists believed this would more likely occur in less developed state with weaker nationalist ties, such as Russia, where the revolution would be guided by the dictatorship of the proletariat.

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Further, traditional Marxists would often have a focus upon mass collective organisation, whereas Leninists in the pre-revolutionary days supported a policy of maintaining a tighter, more secretive and elite cadre of revolutionaries. This is represented to some extent with the split between the Mensheviks and Bolsheviks. An additional difference is that Marxist-Leninism tends to have a much more pronounced and explicit use of both targeted and indiscriminate violence in the application of political agitation and terror. These are just a couple of the differences, which I'm sure somebody else will be able to illustrate more definitively.

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Some sources on theory, and practical application in history:

Orlando Figes, A People's Tragedy

Vladimir Lenin, State and Revolution

Leon Trotsky, An appeal to the toiling, oppressed and exhausted people of Europe

Marx and Engels, the communist manifesto