Once brought to the Americas, Africans would be put in a cell until auction. When ready for auction white men would walk them to the market. The women would be bound together by rope. The men would have chains around their necks and were cuffed in pairs. They would be like that the whole way there, until they were close to market.
They had many slave ships go to where they lived and just kidnap them and bring them to the Americas. They brought them on board and would put them all under the deck. They were packed and cramped together. The men and women were put into separate rooms, the children with the women. Occasionally, only the women and children would get to go above deck for fresh air or exercise.
Families would be split apart. When in auction the buyers would pick the ones that could get the job done, and are affordable. If a buyer wanted a kid, but not the mother than they only got the kid. The children would be forced away from their families, never to see them again.
Harriet Beecher Stowe. She was a women against slavery and she even wrote a book focused on the national attention on slavery, based on runaway slaves and abolitionists.
Not all countries agreed with slavery. Take the British for example, they ended slavery relatively early. After they ended it there they would send ships out to sea to stop slave trading operations.