The purchased them at slave auctions. Owners that had more slaves than they needed, and those bringing them from Africa would sell them at slave markets.
Slave owners sold their slaves to earn extra money. They often bred their slaves so that they did not need to waste money on buying more slaves. When the baby slave was born, they were sometimes sold...
Slaves were considered animals, so they were not treated human. Slaves who worked and lived on plantations were the most frequently punished. Punishment could be administered by the plantation owner...