Had Germany succeed in annexing the Soviet Union, it would have followed a colonization strategy the SS and various ministries had drawn up called Generalplan Ost under the direction of Alfred Rosenberg and Heinrich Himmler

The Soviet Union would have been divided into 4-5 Reichskommissariats, one for the Baltics (Ostland), Ukraine , Moscow and the Caucasus.These Reichskommissariats would be virtually controlled from Berlin, with local population getting virtually no autonomy, as their purpose was eventual integration into the Grossgermanisches Reich (Greater German Reich).They also vary in size and breath depending on what account you find ,and because the Nazi's destroyed all the original plans, we will most likely never know. Once occupied, the next step would have been the gradual elimination of the local population of the Reichskommissariats. This was done be done in many ways, from forced migration, the gradual elimination of undesirables via the concentration camps system (which would have almost certainly been expand massively in the wake of the Soviet Union's collapse), to the infamous Hunger Plan, in which the German would engineer a famine by seizing virtually all food produce from the local population. They had already implemented this on a smaller scale in the Ukraine and Poland to much effect.^1

Overall, the Generalplan Ost called for anywhere between 35-45 million^2 people to be killed right across the occupied territories in the East in order to make room for a projected 8-10 million German settlers, who would have been mostly placed in the most fertile Ukraine and Don basin. Overall, the entire process was predicted to take up to 20-30 years, and would see the complete Germanization of the Ostland and the full occupation of the Lebensraum that Hitler so desperately desired for the German people

(1.Adam Tooze, The Wages of Destruction, Viking, 2007 2. John Connelly. Nazis and Slavs: From Racial Theory to Racist Practice)