To make tofu from soybeans, soybeans are first soaked in water to soften them, then grated and slurped. The resulting product is called "go," and water is added to this "go" and heated over a fire before it is put into a cloth bag and strained. The liquid that comes out of the cloth is called "soy milk. This is literally like milk made from soybeans.
When nigari is added to the soybean milk, the soybean milk curds up to form tofu. However, as it is, it is just a lump, so it is put into a rectangular box and neatly packed. This is the approximate process of making tofu.
In actual production, a little more attention to detail is required, but it can be done at home.