You had forced labour, where workers from occupied territories were forced to go work in Germany's food and production industries. Some nationalities were treated better than others, but most got back home alive. A lot of dutch men forced to work in Germany described it as none too bad times. It was forced labour, but they were fed and treated well enough by their employers. Most were even paid (very low) wages.
Then you had the labour camps for jews, gays, political opponents, resistance fighters and other people deemed unworthy of life. Work was hard, food was scarce, diseases killed many who were too weakened. Their main purpose was still labour, not extermination. Slaves were fed more if the supply of slaves was low. Having all your workforce die is bad for productivity.
Then there were the extermination camps for jews, gays, gypsies, and of whomever more the nazis regarded extermination to be the main goal.
Most extermination camps had a labour department, why waste good muscle if you can waste it off by labour, right?
The infamous 2-way split in Auschwitz at the entrance is exemplary. Upon arrival by cattle wagons at the Auschwitz train platforms, people would stand in line, Mengele and his staff would look at them, decide if they were fit for labour, or could maybe be used in medical experiments. Those that were picked went to the left, to be de-liced with chemicals, shaven bald, and were allowed to work themselves to death. Or treated very precisely with scalpels to determine for veins in the body how long it takes a human to bleed to death from. Those that weren't picked went to the right, following a road straight from the station to the gas chamber entrances.
The labour department of extermination camps was pretty small compared to the genocide industry.
At it's peak efficiency, Auschwitz could gas 20 thousand jews per day. It could handle more, but train transport couldn't supply more.
Out of 1.3 million people sent to Auschwitz, 1.1 million were murdered. Most on the day they arrived.