Learn Spanish (Spain): La novela trata de una familia muy rica.

While you will sometimes hear es sobre, trata de is the most natural and common way in Spanish to say that a book, movie, or story "is about" something. It comes from the verb tratar (to treat or deal with).

I've also learned "tratarse de" means "to be about". Why isn't it "se trata de" here?

We use the non-reflexive tratar de when the subject is specifically mentioned right before it, like La novela in this sentence. You use the reflexive tratarse de when there is no specific subject, usually translated as "It is about" (for example, Se trata de una familia).

If I add a verb after "trata de", does it still mean "is about"?

No, and that is a great thing to watch out for! If you use tratar de followed by an infinitive verb, it means "to try to" do something. For example, Trata de escapar means "He tries to escape."

Doesn't the word "rica" usually mean "tasty"?

It depends on what you are describing! When used with food, rico or rica means "tasty" or "delicious." However, when describing people, groups, or countries, like una familia muy rica, it means "rich" or "wealthy."