African Slaves were taken to the west of the continent to be loaded onto the ships. Now they began the horrible, "middle passage."
This middle passage went from Africa to either North America, The West Indies, or South America. During this trip they were forced to endure terrible things.
Inside the ship were hundreds of slaves, cramped together. This combined with the heat led to near suffocation, horrible smells, and diseases that would spread quickly. Many died on this horrific trip.
Once the surviving slaves made it to their destination, they would be put to work immediately, harvesting all the land. When they got all the raw materials, mainly including, cotton, rum, and more firearms, they would deliver them back to Europe.
These raw materials were taken back to Britain fulfilling there horrible wishes. After they received these things they coudn't get in Europe, the would repeat the trade, trying to maximize their economical benefits.