Gumbo is not soup~
First off, If you want to make gumbo, first you make a ROUX~
Use equal amounts of fat (usually veggie oil) and flour to make a roux. Heat your oil (start off at low/med high if you are a beginner) in a nice skillet like a well seasoned cast iron, then add the flour and stir with a whisk. It willbegin to change color from a "blond" roux until it is a very dark brown. Continue to stir until it reaches a nice dark peanut color or even darker (remember when you add the veggies it will lighten up the roux), and do not leave the mixture or it can burn quickly, and if that happens you have to throw it out and start all over again.
At this point, you can either add the veggies or store the roux in a covered jar for use at a later time. It will keep in the frig for weeks! You can use a roux in your gravies as needed.
Add your veggies to the hot roux, and stir until veggies are wilted, then add your seasonings (you must also know your seasonings for gumbo)
A blond roux is usually used for an Etouffee, a Creole, or other dishes that should not be dark. Not many folks would add tomato sauce to a gumbo for any reason. Creoles do add tomatoes but not tomato sauce. The Cajuns usually do not add tomatoes to their gumbos, or their Jambalaya.
There is nothing better than a well made roux to make you gumbo taste like it should. The ROUX is what give the gumbo that rich nutty flaver that makes the gumbo delicious.
My family (who are all Creole cooks) makes the best Duck, Crab & Shrimp Gumbo you have ever tasted. Be sure to make a delicious potato salad to go along with your gumbo.
Again, if you want to make gumbo, first you make a ROUX~
Or, you can use the packaged stuff :)