How do humans use ocean currents to our advantage?
Not sure we do anymore, at least not directly.
Before steam ships were invented in the early 1800s , sailing ships would use ocean currents to go to and from the "New World" (North America) and back as they carried goods to Europe and later Asia. Following ocean currents and wind patterns was the only way to go such long distances by sail. Today, modern diesel ships pretty much take the path of least distance and currents aren't as important as they were.
The climate of many countries around the world is influenced by ocean currents as they often bring warm or cold currents close to land and thereby warm or cool climates. For example, the Gulf Stream flows from the sub-tropics in the Atlantic to the east coast of the U.S. (warming it) and then heads off to Europe where it also has a warming influence.