The significance of Lenin is that he was the one who was the leader of the movement that made Russia into a communist country. This changed the entire course of Russian history.
Before 1917, Russia was a monarchy. Its monarchs kept all the power to themselves and tended to be very oppressive. This led many Russians to want to get rid of the monarchy. In 1917, the monarchy was overthrown. There was a conflict as to what sort of government would come next. Lenin and his communists won the conflict and Russia became the Soviet Union, a communist country. This was a huge change in the nature of Russian politics.