Do I need to run CRA when working on downloaded file?

Hi, it is pretty embarrassing, but I am kind of lost…Do I need to run CRA if I want to work on an app which I downloaded (I’m working on Emotion project from CodeCademy course, and I GET npm ERR! Missing script: “start” after running “npm start”.
I followed instructions and only ran one command prior to “npm start” - “npm install”.
P.S. I did run CRA in the end and tried to open the app, but got the same message.