Soy sauce has been around a long time, about 2200 years.
While there is some variation, most soy sauce is made the same way. Soy, wheat or other grains are cooked and crushed and then mixed with Aspergillus spore. Then it is mixed with salt brine or coarse salt and left to brew. After fermentation, the mixture is pressed to remove the solids. Then it is pasteurized and filtered. Finally, the soy sauce is bottled.
Japanese soy sauce is known as shoyu. Most are a blend of wheat and soy, which results in a flavor that is thinner, sweeter and less harsh than Chinese soy sauces. Tamari is Japanese soy sauce that is closer to the Chinese style, and often has little to no wheat.
There are 2 main kinds of Japanese soy sauces, light and dark.
Dark soy sauce is called Koikuchi.
Most supermarket brands are considered to be dark soy sauces. They are often fermented quickly. Really great soy sauce is aged in cedar barrels for up to a few years, creating a complex flavor.
Dark soy sauce can be considered as an all purpose soy sauce, great for marinades and dipping sauces.
Light soy sauce is called Usukuchi.
Light soy sauce has an intense flavor, even though it's lighter and thinner than dark soy sauce. They are great for seasoning dishes without changing their color.
Tamari is a thick, dark soy sauce.
Miso is made by mixing Koji (a blend of rice and Aspergillius spores) with cooked soybeans and salt, and letting it ferment. A rice dark liquid forms on the top, and can be drained off. This is how tamari is made. Many tamari soy sauces can still contain traces of wheat, but some companies offer gluten-free versions.
Tamari's light version is shiro, which is brewed with more wheat. Saishikomi is twice brewed soy sauce, made by using a previously brewed batch of soy sauce instead of brine. As you can imagine it has a stronger flavor than tamari.
Ponzu is a blend of soy sauce, vinegar and citrus juice, often yuzu.
Ponzu is a blend of dark soy sauce, citrus juice, rice vinegar, mirin, katsuobushi flakes, and kombu. It is a bright and delicious dipping sauce for meats, fish and even dumplings.
Shiro Dashi is a seasoning made from light soy sauce and dashi.
This is a concentrated seasoning is used to bring saltiness and umami to your dishes. Often made into a broth by diluting it 1:10.