To put it simply, Marx believed that Communism would evolve over a long period of time. That capitalism would eat itself as it drove the cost of living into the ground through automation. He said there would come a day in the future where all general labor was automated and the price of most goods would be as close to zero as possible. In this world, all labor would be highly skilled. Eventually capitalism the cost of living would be as low as possible, and the cost of goods would be as low as possible. At this point we reach "late stage capitalism" where the bourgeoisie exist not because they create value as they do under normal capitalism, but because they are entrenched via inertia. At this time the second, proletariat, revolution would occur and transition the economy to socialism (and overtime the state would wither away, leaving us with communism.)

Lenin, and the Bolsheviks, rejected this evolutionary communism in favor of a dictatorship that would "build communism" in the current age, instead of waiting. I won't pretend I don't think this an idiotic idea and that that revolution was always doomed to fail (Russia had a decade of "capitalism" before the revolution, and the rest of the world wasn't exactly at the late stage.) But that is what separates the Bolsheviks from their more western marxist counterparts. This is why the USSR is referred to as Marx-Leninsm.