Well, for starters he ordered the execution of the royal family after Nicholas II peacefully abdicated the throne and allowed himself and his family to be arrested. He also outlawed other political parties. He used Leon Trotsky as a sort of one man goon squad, sending him around the countryside prior to collectivization to bully around the peasants to see how much resistance they might put up. He formed the Cheka, which were the forerunners of the KGB, and used them to root out potential political competitors and have them gotten rid of.

If you're interested I can recommend a few pretty good books on Russian history.