Charlie,
Miso soup is very easy. Real miso soup has 2 essential components: Miso and dashi. You need both.
You have the miso. I prefer white miso for soup but some people like yellow or red.
Dashi is a broth made with both dried bonito (fish) and dried kombu (kelp seaweed).
You can find the bonito and kelp at some asian markets -- to make your own broth. Or you can buy dry dashi granules like boullion powder. The dry stuff should be in most asian markets. It comes in both jars and foil packages.
For every quart of dashi broth you use, dissolve about 1/4 cup miso paste. Or to taste.
Good additions are tofu, shitake or wood ear mushrooms, scallions, lbster, shrimp, etc.
Vegetaraians make miso soup without the dashi, just using the kombu.
You can skiop the dashi but it won't taste anything like real miso soup.