Short answers, pulled from the story.
There were 27 main camps and, according to historian Nikolaus Wachsmann, more than 1,100 satellite camps. Historian Karin Orth estimates the number of subcamps grew from 186 at the end of 1943 to at least 662 by January 1945.
The first Nazi concentration camp was Nohra, established on the 3rd of March 1933 in a school building. It was opened within weeks of Adolf Hitler becoming chancellor of Germany on the 30th of January 1933.
About 1.65 million people were registered as prisoners, of whom nearly a million died during imprisonment. Including the approximately one million Jews gassed on arrival at Auschwitz without being registered, the total death toll is estimated at between 1.8 million and more than two million.
The camps were administered by the SS through the Concentration Camps Inspectorate, headed by Theodor Eicke from December 1934. The inspectorate was later subordinated to the SS Main Economic and Administrative Office in 1942. Heinrich Himmler retained direct authority over the system throughout.
Dachau served as the organizational model for all subsequent camps. Theodor Eicke, appointed its commandant on the 26th of June 1933, drafted the Disciplinary and Penal Code that standardized punishments and created the prisoner-functionary hierarchy used throughout the system.
Private companies could hire prisoners from the SS for a daily rate of 3 to 6 Reichsmark, roughly half the wage of a free worker. By 1943, two-thirds of prisoners worked in war industries. Historian Marc Buggeln estimates that despite this, concentration camp labor accounted for no more than 1 per cent of Germany's total arms production.