Plantation owners, who needed slaves to work on their plantations or help in the house, went to a slave auction.

At

this auctions - these auctions, better: At auctions like these

you could buy both slaves  who were just brought to America and slaves who had already lived there. You could choose exactly the kind of slave wich you needed: strong slaves for the fields, female slaves for cooking, etc.

The slaves

often were sold  - word order: were often sold

by plantation owners who didn't need them anymore or who needed money, e.g.  to pay their debts.
Families had to break up if maybe the son was sold to

an other man - to a different plantation owner

 than the mother.
The sold slaves had to go wherever their new owners wanted to bring them and had to do whatever they wanted them to do!
Slaves were treated like objekts!

Daniel + Lara