The first method is to make salt by digging out chunks of salt called rock salt from the ground, breaking it down, and sifting it. Although not found in Japan, there are places in the world where salt is extracted from rock-like chunks of salt from beneath the ground.
The second method is to draw salt water from a pond or lake. There are no saltwater ponds or lakes in Japan, but there are saltwater lakes and ponds in the world that are many times larger than the oceans. We pump up those brine lakes and ponds, heat them, evaporate the water, and extract the salt.
The third method is to use water from the sea. In the past, sea water was spread on the soil and heated by the sun to extract salt. Some places still use this method to make salt, and salt made this way is reputed to be delicious.
The disadvantage of this method, however, is that not much salt can be produced. Nowadays, salt is made by pumping up water from the sea with a machine, and salt is produced in factories.
In Japan, salt was and still is made by the third method, using water from the sea. This is because there is no rock salt or salty lakes in Japan. Instead, Japan is surrounded by the sea, so using water from the sea is the best way to make salt.