Miso soup is a traditional Japanese soup, contains Dashi (Dashi = fish stock or broth), miso paste, tofu (bean curd), seaweed (nori or wakame), onions, mushroom, seafood (tuna,octopus,shrimp) and scallion/spring onion. Other ingredients are different from place to place (potatos, carrots, daikon=winter radish)
The "Dashi" soup stocks for miso soup can be from niboshi (dried baby sardines), kombu (dried kelp seaweed), hoshi-shiitake (dried shiitake mushroom) or Katsuobushi (shavings of dried and smoked bonito flakes, aka skipjack tuna).
The "Kombu" can also be used in combination with dried shaved tuna or dried shiitake mushroom. The kelp seaweed and/or shiitake dashi is usually served for vegetarians.
Miso paste looks like this: