One, of many, articles describing the difference: https://www.forbes.com/health/body/cacao-vs-cocoa/
> “Think of cacao, cocoa and chocolate like a pipeline,” says Fazio. “Cacao [fruit] grows from a tree and is raw and unprocessed. It’s the precursor to cocoa, and cocoa is the precursor to chocolate.”
> “The taste of cacao is earthy and bitter, and it has a grittier mouthfeel than chocolate,” says Fazio. “Cocoa powder tastes more like chocolate than cacao, but it doesn’t have a creamy mouthfeel either because most of the cocoa butter has been removed.”
> Some experts use “cacao” for the pods, beans and ground-up contents of the beans, reserving “cocoa” for the powder left after pressing the fat out of the ground beans (1Trusted Source).
Cocoa is post processing, in the way to make chocolate.
It might be best for you to purchase both and taste. Cocoa tastes like chocolate, Cacao is kinda earthy and bitter. They cannot be substituted for each other in recipes.
In my country there isn't even a thing called cocoa, it's all cacao with a k, kakao. Kakao beans, kakao powder etc. There is something called cocholate powder which is kakao powder mixed with milk powder and sugar, but I don't think that's what you are talking about.
I might buy some raw kakao/cacao beans to see what happens if I crush them.