Making a fish stew sounds daunting, but it's only marginally more difficult than making a peanut butter and jelly sandwich. (Actually, if don't have peanut butter, fish stew is easier.) You'll only need a handful of ingredients and, for the most part, any fish or shellfish (a combination is best) works.
First, heat some olive oil or butter in a soup pot. Add some chopped onion and cook the onion. You don't want the onion to brown, so stir occasionally so it becomes translucent (and sweet). When the onion starts to soften, add some minced garlic and continue the now-and-again stirring.
When the onion and garlic are soft, add a can of diced or whole peeled tomatoes and two cups of water. (For fish stew, I use a 28-oz. can of Bionaturae's organic diced tomatoes in BPA-free cans.) Add a little unrefined sea salt and fresh ground pepper; if you have thyme (fresh is great, dried is fine) add that as well. Bring the mixture to a boil (keep stirring occasionally) and then lower to a simmer for about 15 minutes.
One problem home cooks have is overcooking the fish, so make sure to stagger the addition of the different fish, depending on their cooking times. For example, in the fish stew I just made, I used live clams in their shells, cod, weakfish, shrimp and scallops (out of shell). Cooking time of the clams always seems to take longer than the other items (which I cut into smaller pieces), so I added the clams first. When their shells open, they are done. As they opened (not necessarily at the same time), I removed them to a bowl.
After this, I added the other seafood and immediately turned off the heat. The liquid was hot enough—and the fish so delicate—that everything was cooked through in three or four minutes. I added the clams and let the stew sit for about 10 minutes, both to cool and to let the flavors develop. I tasted and added a touch more salt. A little chopped parsley added color, flavor and nutrition.
One more point: Many fish stew recipes call for fish stock. I know this may be sacrilegious, but I think it's unnecessary and a waste of money. Quality seafood will contain all the fish flavor you'll need.