The first extermination camp was at Chelmno. It began large-scale routine (as opposed to experimental) gassings on 8 December 1941, using sealed vans with the carbon monoxide exhaust diverted into the vans. The total death toll at Chelmno is estimated at about 152,000-153,000 and there are only two (!) known survivors.
Concentration camps, originally established for political prrisoners, had been established already in March 1933. Dachau, near Munich, was the first concentration camp. It had a high death toll but it was not an extermination camp.