It was formed in 1565 to give Ivan a section of territory in which he could be free from noble interference and rule as a completely unlimited autocrat. The Oprichina contained much of Russia's best land, including Moscow and many of the large central cities. The rest of the Empire was referred to as the zemshchina; these areas were ruled by powerful boyars.
The Oprichina was administered by the terroristic Oprichniki, who used extreme violence against any opposition to Ivan's rule. This included both nobles and peasants. During the era of the Oprichina these Oprichniki killed thousands and devastated the area.
The Oprichina was a total failure and Ivan was forced to disband it in 1573. What had once been Russia's best and most fertile areas had been devastated and had fallen well below the rest of the country. Those that had not been killed by the Oprichniki often fled into other areas of Russia. Instead of increasing (as Ivan had hoped), tax revenues fell, and Russia was badly prepared when the Crimean Tartars attacked in 1571.