Ocean water cannot be used for anything by humans.
Ocean/sea water cannot be used for drinking but it can be used for many other purposes also i.e., for obtaining salt, as it is a massive water body we can travel from one plane to another by ships. Oceans can also be used for trading, transportation etc. But nowadays many steps are taken to make the sea water clean, the process of purifying sea water into fresh water is called desalination, which essentially means removing the salt from water.
The oil-rich middle east countries have hardly any source of fresh water, it hardly rains over there and there are no rivers. The famous city of Dubai, for example, has some of the world's largest desalination plants to purify sea water into fresh water.