Most of the time the slaves had to do the hardest work their boss had for them. Most common things were working in the dark and dangerous mines and on the cotton plantations. When they didn't do their job well enough they were punished severely. They were hit and died shortly after becoming a slave.
There was a group of slaves who were luckier, if you can call it luckier, they became a slave of a famous artist or somebody of equal status as their owner. Then they didn't have to work that hard and were treated a lot better. Most of the time they lived longer and in better conditions. They had to do all sorts of small jobs around the house, like doing the dishes, cooking, the garden and other sorts of domestic work.
A third thing slaves could do was fight in an army. It was a great solution they thought, because it didn't matter if a slave died and nobody really cared (except other slaves of course). When the war was over they had to do other jobs such as weaving.
Most of the time, especially when a lot of slaves worked together, there was a leader with them who told the slaves what to do. Sometimes they were chained to each other or their workplace. To make the work easier they wrote songs to sing while working. Some of them are still sung and have become very famous, so it reminds us of the bad history of the slaves.