Gumbo is a method, not a specific dish. I just made turkey gumbo using leftovers from Thanksgiving. You can make a good gumbo out of almost anything, if you keep a few basic principles in mind.
First, you will need some Cajun seasoning. This is a combination of paprika, onion powder, garlic powder, salt and pepper, along with other herbs as the cook deems suitable. Dried thyme and oregano most often turn up in seasoning mixes. You will also need bay leaves.
The second component of a good gumbo is the combination of aromatic vegetables that has come to be named "trinity" by many cooks. It consists of roughly equal parts of chopped onions, celery and green bell peppers.
Fresh garlic is almost always included in gumbo, too, along with tomatoes. In winter, canned tomatoes are fine. You also need stock, ideally one that matches the main protein in your gumbo, i.e., chicken stock for chicken gumbo, pork stock for pork gumbo, etc.
Assemble those components first, then heat some fat in a large kettle or Dutch oven over medium low heat. Brown any raw meat or sausages that you intend to include. Cooked meats and seafood, if you include them, are added at the end of the cooking, not the beginning. Removed the browned meat to a heatproof bowl and reserve it. Add half of the trinity to the pot and cook, stirring once or twice, until the onions are translucent. Add some seasoning mix and the rest of the trinity, and continue to cook until some of the onions are lightly browned. Add bay leaf and garlic and stir for 30 seconds. Add tomatoes with juices, and stir well, scraping up any browned bits on the bottom of the pot. Add more seasoning mix, then cook gently until most of the liquid has evaporated.
Add stock to the pan and bring to a simmer, stirring occasionally. Add the browned meat and any other protein. Simmer long enough to cook shrimp or any other seafood you have added. Add a dash of Worcestershire sauce, and serve the gumbo hot with rice. Garnish with chopped parsley or green onions if you wish. Pass hot sauce.
You will note that this method does not involve thickening the soup. If you like it thicker, you can add fresh or thawed frozen raw okra, or use a roux. Add the thickening ingredient after the stock simmers, stirring well until the soup is smooth and bubbling. Then add seafood or other proteins.
Once you have mastered this technique, you can create a gumbo any time you like, using seasonally fresh ingredients.